I can't even count how many times I've been told, in all seriousness, that there are more liberals than conservatives in academia because liberals are simply smarter. I pity anyone who tried to use that reasoning to explain why there are more male than female engineers. Megan McArdle points out that the simple "explanation" that continually comes from academics is a serious blind spot.
In blog years, this is an age-old argument. I find it particularly intriguing because it completely reverses the standard argument about discrimination. Conservatives are usually reluctant to agree that women and minorities are still often victims of structural or personal bias--despite numerical underrepresentation and some fairly compelling studies showing that hiring is not race or gender blind. Yet when it comes to conservatives in academia, they suddenly sound like sociologists, discussing hostile work environment, the role of affinity networks in excluding out groups, unconscious bias, and the compelling evidence from statistical underrepresentation.
Meanwhile, liberals, who are usually quick to assume that underrepresentation represents some form of discrimination--structural or personal--suddenly become, as Haidt notes, fierce critics of the notion that numerical representation means anything. Moreover, they start generating explanations for the disparity that sound suspiciously like some old reactionary explaining that blacks don't really want to go into management because they're much happier without all the responsibility. Conservatives are too stupid to become academics; they aren't open new ideas; they're too aggressive and hierarchical; they don't care about ideas, just money. In other words, it's not our fault that they're not worthy.
Academics should also consider that the under-representation of conservatives among them creates a significant image problem that leads to dismissal and mistrust of the academy by the general population.