Conservatives often prove to be their own worst enemy in the arena in free speech.

Bloomberg contributor Francis Wilkinson takes a look at what this means on college campuses, especially in the context of “epistemic closure”.

Kevin Hassett of the American Enterprise Institute did some data collection in the Los Angeles Times:

“I looked at commencement and other announced graduation event speakers for 2012 and 2013 from the top 100 universities and top 50 liberal arts colleges (according to the U.S. News & World Report rankings).”

All told, he wrote, “there were only three identifiably conservative speakers at the top 50 colleges and 12 at the top 100 universities, compared with a total of 69 identifiably liberal speakers.”

Like conservatives before him, Hassett concludes that liberal arts colleges are “hostile territory.” One of his case studies is especially convincing. Robert Zoellick, the U.S. Trade Representative and a deputy secretary of state for President George W. Bush, who later served as president of the World Bank, withdrew from a scheduled commencement speech at his alma mater, Swarthmore College, after students objected to his association with the Bush administration. As Hassett wrote:

“If Zoellick, a moderate gentleman with an impressive record promoting women’s rights as president of the World Bank, can’t speak on a college campus, no Republican can.”

If liberal colleges can’t tolerate the likes of Zoellick, they really do have a problem. But the overall numbers may be due to another factor beyond rude liberal students plugging their ears: It keeps getting harder to find conservatives worth listening to.

In the past couple years there has been much blogosphere discussion of “epistemic closure” on the right — the phenomenon of conservative media, politicians and intellectuals forming a closed information loop in which they more or less tell one another what they like to hear.

The resistance of liberal campuses to inviting conservative speakers confirms the phenomenon isn’t purely a product of the right. Yet in Washington and on the Internet, it overwhelmingly is. (The obvious caveat: Conservatives like Ross Douthat and Ramesh Ponnuru continue to rise above the dreary mean, though it must get pretty exhausting for their small, hardy band to hold up the entire side.)