It’s not (contrary to what you leftists think) because they’re stupid. It’s because you are:

Perhaps the most problematic aspect of Green’s post is that, despite what he believes, most conservatives do not complain about liberal bias on American campuses because they are full of people who believe that evolution is true or that the US lost a war against Vietnam. They complain about liberal bias on American campuses because they are full of people who think conservatives are just cretins who are incapable of forming their beliefs in a rational way and have no problem saying so on a regular basis. In short, they complain about liberal bias on American campuses because they are full of ignorant fools like Green, who know next to nothing about what conservatives actually believe. Green’s lazy rant is a perfect illustration of why it’s hard to be a conservative on campus. Of course, he didn’t do it on purpose, but that doesn’t make his post any less valuable.

…This bias is a real problem that should concern everyone and deserves better than Green’s idiotic post. I’m one of a handful of openly right-wing people in academia, so I’m in a particularly good position to talk about it. In my experience, people who aren’t conservative have no idea what kind of things those who are have to deal with in academia on a daily basis, which is part of the problem. Universities worry a lot about micro-aggressions, implicit bias, etc. against women and minorities. But there is nothing “micro” or “implicit” about the hostility conservatives have to face on campus. Nobody goes around campuses saying that women and black people are stupid, but not a day goes by on campus without people saying that about conservatives. In my field, conservatives are so afraid to speak up that some of them have created secret groups, where they can say what they think without fear of reprisal. Just think for a second about how toxic the environment must be in order for things to have come to that.

This is of a piece with Haidt’s work that showed how conservatives easily understand leftists, but leftists are clueless about what conservatives believe.