In a recent column at the Washington Post, Eugene Volokh describes the lack of intellectual diversity in higher ed.

Universities only seek certain types of diversity

Georgetown University professor John Hasnas writes in the Wall Street Journal of his experience with faculty candidate searches over the past twenty-plus years. Not only is there rarely any effort consider ideological or viewpoint diversity, but in some cases there have been efforts to squelch it.

in my experience, no search committee has ever been instructed to increase political or ideological diversity. On the contrary, I have been involved in searches in which the chairman of the selection committee stated that no libertarian candidates would be considered. Or the description of the position was changed when the best résumés appeared to be coming from applicants with right-of-center viewpoints. Or in which candidates were dismissed because of their association with conservative or libertarian institutions.

Most folks who have been in the academy for a significant period of time are aware of such stories (or have seen them first hand). And given the nature of faculty hiring, it is generally easier to sink a candidate than to see them through. So if one member of a faculty committee refuses to hire someone because the candidate clerked for Justice Clarence Thomas (true story) or refuses to admit a graduate student because he had received an Olin fellowship (another true story), that’s often enough to end the candidacy.