For a helpful explanation for why this ‘bias’ exists in academia, read this post by Joe Heath (a philosopher at the University of Toronto).
One of Heath’s key points is something that I’ve long held to be obviously true—viz., universities are inherently ‘pro-reason’ (broadly understood to mean an overall pro-evidence, pro-argument, pro-logic, etc., outlook). So insofar as much of political and social conservatism is anti-reason (anti-evidence, etc.), then academia inevitably is going to be a hostile environment for most political and social conservatives. And to the extent that anti-reason conservatives go to university and become less conservative as a consequence, this is not (or at least not primarily) due to ‘brainwashing’ by Marxist profs, but rather because they become acclimated to a rationalist way of seeing the world. (In contrast to anti-reason conservatives, libertarians are massively overrepresented in academia, especially in the US. But of course libertarians think that they have arguments for their positions; they’re ‘pro-reason’, like their liberal and left-wing interlocutors.)
Another thing that I like about this post is Heath’s take down of the irritatingly influential Jonathan Haidt. What I find most grating in much of Haidt’s work is its unargued premise of moral non-cognitivism. (Heath also criticizes Haidt’s ‘political moralism,’ which strikes me as fair, but is not something that causes me to tear my hair out in annoyance.)