Here is a verboten thesis outside value theory, though one I think is worth exploring. Godel’s version of Peano Arithmetic (PA with Godel numbering) is inconsistent.
To question Godel is to question one of our high saints, and an unestablished member of the profession would probably be marginalized (to a large extent) for doing so. (Who are YOU to question Godel’s achievement??) Even so, everyone grants that Godel’s proof establishes incompleteness only on the assumption that the system is consistent. (Yet per the second incompleteness theorem, you can’t prove consistency within the system. And long story short, to prove consistency in a different system assumes the consistency of the second system.)

I have a hard time thinking of much of anything these days that meets your explicit qualifications. There are plenty of areas of philosophy that are low-status, and so faculty are worried about working on issues that fall under them. Recall that interview with Jonathan Ichikawa that you linked to recently, where he explicitly says that now that he has tenure, he wants to turn some of his attention to issues arising from photography. It’s probably too much to characterize that as “fear”, but the reticence and the worries behind it are real, and the result is probably not so great for the philosophy of art in general.

The best case I can think of that meets your criteria is one that’s no longer really an issue: paraconsistent logic before Graham Priest made it respectable.

The following “observation” struck me:

“[W]hen these [poor philosophical treatments] are rejected or harshly criticized, one might mistake that as a criticism of having an unpopular view, rather than criticism for having a poorly defended view, and one might become fearful of being open about expressing the view. The solution to this is argumentative rigor informed by interpersonal sensitivity. It isn’t an easy or guaranteed solution. But it can go a long way towards getting unpopular ideas taken seriously. This does not mean that all such ideas will get taken seriously: some ideas have nothing going for them besides some easily refutable opening gambits. But with the right approach, more could.”

Remember that the kind of person most at issue here is someone who holds a certain unpopular view and thinks that academic philosophy is unfairly hostile to those who hold that view. Obviously such a person isn’t going to think that the unpopular view in question has no good evidence behind it. Nor is he likely to think that existing defenses of it (quite possibly including his own) simply suffer from a lack of argumentative rigor or interpersonal sensitivity. After all, the very problem he alleges to be present is that even if one *does* defend the view rigorously and with appropriate interpersonal sensitivity, one will *still* be liable to face ostracism, ridicule, and vilification; that, I take it, is largely the thought behind the idea that such responses are unfair. Now, whether this person’s charge is plausible is one question. But the present point is simply that that is what he does think, and what you’ve said doesn’t seem to address it (which one might have thought from its being framed as an “observation”) so much as condescendingly deny it. I imagine such a person having more or less the following reaction to what you’ve said (though perhaps he would phrase it more politely):

“Oh, of course! *That’s* what the problem has been this whole time: poor philosophical treatments! Thank you, Justin–why didn’t I think of that? For someone who, by all indications, has never had the experience of holding the unpopular view in question, you sure do have a keen insight on these matters. Silly me–I actually thought that the view had merit and that the existing defenses of it were quite good, and that people were just reacting to it unfairly harshly, but now I see the truth. If I had just followed your ‘solution’ of ‘argumentative rigor informed by interpersonal sensitivity,’ I would never have encountered such hostile backlash. People would never have thought of me and spoken to me as if I were a horrible person the moment I voiced sympathy for the view. It was all just my own philosophical blunders and insensitivity that were to blame! From now on I’ll make sure to be more rigorous and sensitive. And if people *still* react to me with contempt and ridicule? Well, as you’ve so wisely implied, Justin, that just shows that the view has nothing going for it ‘besides some easily refutable opening gambits.’ I guess that settles it!”

At the risk of belaboring the point, let’s imagine an example from another context. Suppose that some feminists claimed to be unfairly ridiculed and vilified in academic philosophy for holding feminist views (e.g., people immediately assuming that they’re anti-male bigots and subsequently wanting nothing to do with them). Imagine, further, that I had just written a blog post soliciting such people’s thoughts and experiences to try to get a better sense of just what the problem, if any, might be. Now imagine that I followed up the initial blog post and comment thread with this:

“Feminism concerns the identity, status, and treatment of people. Some of these people are your colleagues, students, and acquaintances. I am not surprised then, that feminist views are among those that some people claim to be verboten.

“A person either will or will not have some trepidation about insulting or undermining or harming one’s colleagues, students, and acquaintances (or doing things which might readily be perceived as such). If one does, then that might register as a kind of fear. If one doesn’t, then one is likely, I believe, to approach these topics in a naive or incomplete way, which will result in poor philosophical treatments; when these are rejected or harshly criticized, one might mistake that as a criticism of having an unpopular view, rather than criticism for having a poorly defended view, and one might become fearful of being open about expressing the view.

“The solution to this is argumentative rigor informed by interpersonal sensitivity. It isn’t an easy or guaranteed solution. But it can go a long way towards getting unpopular ideas taken seriously. This does not mean that all such ideas will get taken seriously: some ideas have nothing going for them besides some easily refutable opening gambits. But with the right approach, more could.”

I think it’s fair to say that this would not do anything to engage with the concerns of those whose experiences I had solicited. The present situation seems to me analogous.

Still, I appreciate that you’re continuing the discussion in some form.

The kind of views that are likely to get one into trouble are mostly in politics, political philosophy and ethics. In philosophy of science, questioning evolution is likely to have some negative consequences. Whenever I say anything critiquing evolutionary theory I hedge a lot, as I know the risks.

However, more generally there is a phenomenon where popular views have lower standards of argumentation than unpopular views. Look at Mackie’s almost totally question begging argument from queerness, for example. It assumes a kind of materialist view of the universe that his opponents are likely not to hold. However, as materialism is the orthodox position, this is allowed. However, imagine someone trying to do the opposite? Imagine an argument that assumed a non-materialist view of the world?

I think this is a prime example of a double standard in philosophy more generally. Mackie can assume a world view in his argument against moral realism that many of his opponents would reject, but his opponents cannot assume their worldview when arguing against the error theory. In other words, the queerness of moral properties is largely due to a materialist world view that many moral realists are going to reject (I do), but even though Mackie’s argument is question begging in this way, it’s a popular argument. In reality, it’s a very poor argument that if the situation were reversed wouldn’t get the time of day.

I suspect that the project is essentially a hard one.

There’s some really easy examples that no one’s going to mention. For instance, consider the following views: knowledge is a mental state that belongs only to inanimate objects; truth is a property of sentences in English but not French; what is morally right is that which is endorsed by a minority (and not a majority) of members of the community; the mind is a non-physical substance but thought is an activity carried out only by the brain with no mental connection.

That’s because these views are just patently ridiculous, with no intuitive pull at all. But when we’re asked to list views that get one ridiculed by members of the philosophical community, we’re necessarily going to be listing views that strike many people like ourselves as ridiculous, and thus might strike *us* as ridiculous as well. So they’re going to look somewhat similar to the ones mentioned above.

In applied ethics or political philosophy, there are often going to be major pockets of society that have some non-philosophical motivation to hold various beliefs, so it’s going to be easier to find views that *someone* holds that are ridiculed by the academy. But for these other things it’ll be harder.

Still, I’ll make some attempts (even though all of the views I’m going to list probably have a few academic defenders):

Knowledge has nothing to do with evidence, and everything to do with strength of conviction.

Moral goodness is an objective property with no connection to the well-being of any sentient being.

Natural languages have uncountably many grammatical sentences, including ones that are infinitely long. (Defended in a famous book by Postal and Langendoen, “The Vastness of Natural Language”!)

There is no such thing as the mind and no mental activity.

Hi Justin,

Thanks for the follow-up. I’ll consider your questions in order:

“First, in your view, do you think that those who defend unpopular views *well* face ‘ostracism, ridicule, and vilification’?”

Yes, at least a good portion of the time.

“If so, do they face less of that than those who defend the unpopular views poorly?”

It wouldn’t surprise me if defending an unpopular view well makes one less likely to face great personal backlash. That said, it may only be *slightly* less likely–more in a minute about why I prefer to hedge here.

“If you could provide examples of those who defend an unpopular view well but still face ostracism, ridicule, or vilification, that would be particularly helpful.”

At least two examples come to mind for me. The first is David Benatar, who has been publicly denounced as a bigot for his views. (See http://dailynous.com/2016/03/11/student-faces-tribunal-for-calling-philosophy-professor-racist/ and http://hypatiaphilosophy.org/HRO/reviews/content/174.) (I should also mention, however, that to her credit, one of the co-authors of the Hypatia review later apologized for the personal attack at the end of the piece. See http://www.philosophy.uct.ac.za/sites/default/files/image_tool/images/160/Lindsay%20Kelland%27s%20apology.pdf. Other possibly relevant links can be found on Benatar’s webpage: http://www.philosophy.uct.ac.za/philosophy/staff/benatar/selectedbooks/secondsexism.)

Another example is Theodore Everett, who was vilified on Jezebel (!) and in the comments of a post on feministphilosophers for giving a talk titled “Against ‘Sexual’ ‘Assault’ ‘Awareness.'” (See http://jezebel.com/malignantly-dense-prof-lectures-against-sexual-assau-476428570 and https://feministphilosophers.wordpress.com/2013/04/19/philosophy-professor-argues-against-sexual-assault-awareness/.) Also, students at SUNY Geneseo circulated a petition, ultimately reaching 1,687 supporters, demanding that the administration of the university condemn his talk. (https://www.change.org/p/reaffirm-geneseo-s-commitment-to-saa-and-condemn-dr-everett-s-scheduled-lecture-against-sexual-assault-awareness?utm_campaign=share_button_mobile&utm_medium=facebook&utm_source=share_petition)

Did Everett defend his view *well*? Here I’d say that the question is irrelevant. For, in an important sense, he did not even get a chance to defend his view, much less to defend it well; the backlash came in advance, and was based on little more than the talk’s title. People were outraged not because of what he said *at* the talk; they were outraged because the talk *was being planned*.

A few further points here: First, so far I’ve been considering only the publicly observable consequences. There’s no telling what kind of personal attacks or other vile behavior people may have directed at Benatar and Everett in private. Second, Benatar and Everett have tenure. They’re established. While they might be able to get away from such incidents with their careers intact, what *junior* philosopher of minimal prudence would want to defend views like theirs, given the prospect of being so publicly demonized for it?

Here I’ve offered only two examples, of course. But there are other cases of philosophers being ostracized and vilified for defending unpopular views, and not all such cases (in fact, almost certainly the strong minority) are ones that someone could readily appeal to in an online discussion. In many cases, the hostility will not have been publicly observable. In many cases, the person who faced the hostility will not be able to describe the incidents in much detail, for fear of having his identity found out and subsequently facing harm to his career. For whatever it’s worth, I can say that both of these apply to me, and, by all indications, to some of the others who have been commenting on these threads. I wish I could offer more than this, since vague semi-anonymous testimony is obviously not ideal. But I know for a fact that some of my professors and colleagues read these discussions, so, regrettably, I dare not say more about my own case.

To get a better sense of the depth of the problem, I’d recommend (not just to you, but to anyone interested) simply asking philosophers who defend one or more of the deeply unpopular views in question (if you’re acquainted with any such philosophers) what her experience has been. Has the response to her generally been hostile, etc.? While this may not be a good way of gauging just how widespread the problem is, it could, if nothing else, help us realize that the problem is indeed out there (assuming that that is after all what the responses suggest).

Another point I’d like to touch on here: While it’s not just conservative views that are alleged to be verboten in academic philosophy, it does seem that conservative views are most plausibly among those that are verboten. I say this in large part because–as anyone who’s paying attention can surely see–it’s fairly common in academic philosophy to casually smear conservatives. Any time someone needs a stand-in for “crazies, lunatics, etc.” the go-to option is conservatives. (If you’d like me to give examples, I can, but somehow I suspect that it’s not necessary–this really does strike me as something that most philosophers can probably attest to.) Because the myriad jokes and smears here are often presented as casual asides, there’s an implicit suggestion that despising conservatives is common ground for philosophers. With this background in mind, is it really that hard to believe that conservative philosophers (or even simply philosophers who decide to defend a conservative view here and there) *actually are* treated badly? This touches on something I’ve found baffling about your posts on the matter: It is often with evident disdain that you write about the suggestion that conservatives are disproportionately treated badly in philosophy, as if it’s so hard to believe. But is it really *that* hard to believe? Given how open philosophers generally are about how much they despise conservatives, is it not plausible that conservative philosophers are, in fact, treated poorly?

Note that if we count not just personally directed insults, but the more collective insults described earlier, the hostility to which conservative philosophers could count themselves subject would no doubt increase a great deal.

Again, I’m not conservative, but when it comes to the issue of people being mistreated for their views in academic philosophy, it seems to me that conservatives have a case that is prima facie especially worth taking seriously.

I’ll now briefly touch on the second point you brought up: the appearance that people are using the bias/vilification narrative as a cover for their own lack of argument. It wouldn’t surprise me if this was, indeed, sometimes the case. As to how often it happens, I can only say that it probably depends on which view we’re talking about. (Some views within the category of verboten views are much more plausible than others, after all.) But even when people do use the appeal to bias/vilification as a cover for lack of argument, it seems to me that there’s enough other, independent evidence that bias/vilification is indeed a problem, regardless of whether some are co-opting it for an unfortunate purpose.

Trying to get political dissenters to shut up is something humans do. To think that we don’t have to worry about it in philosophy would be to treat philosophers as being very different from ordinary people. Obviously, not all humans do it all the time, and the degree to which it goes on can be overstated, but if it didn’t go on at all in philosophy, that would be weird.

I suspect you would earn yourself some enemies if you argued that so-and-so canonical figure was actually a second-rate philosopher and shouldn’t be in the canon because so-and-so is hopelessly confusing and gives students the wrong ideas about what good philosophy looks like. But I’m interested to see if this perception of mine is accurate. Thoughts?