“Of course there are biases against evangelicals on campuses,” notes Jonathan L. Walton, the Plummer Professor of Christian Morals at Harvard. Walton, a black evangelical, adds that the condescension toward evangelicals echoes the patronizing attitude toward racial minorities: “The same arguments I hear people make about evangelicals sound so familiar to the ways people often describe folk of color, i.e. politically unsophisticated, lacking education, angry, bitter, emotional, poor.”

A study published in The American Journal of Political Science underscored how powerful political bias can be. In an experiment, Democrats and Republicans were asked to choose a scholarship winner from among (fictitious) finalists, with the experiment tweaked so that applicants sometimes included the president of the Democratic or Republican club, while varying the credentials and race of each. Four-fifths of Democrats and Republicans alike chose a student of their own party to win a scholarship, and discrimination against people of the other party was much greater than discrimination based on race.

“I am the equivalent of someone who was gay in Mississippi in 1950,” a conservative professor is quoted as saying in “Passing on the Right,” a new book about right-wing faculty members by Jon A. Shields and Joshua M. Dunn Sr. That’s a metaphor that conservative scholars often use, with talk of remaining in the closet early in one’s career and then “coming out” after receiving tenure.

This bias on campuses creates liberal privilege. A friend is studying for the Law School Admission Test, and the test preparation company she is using offers test-takers a tip: Reading comprehension questions will typically have a liberal slant and a liberal answer.

Some liberals think that right-wingers self-select away from academic paths in part because they are money-grubbers who prefer more lucrative professions. But that doesn’t explain why there are conservative math professors but not many right-wing anthropologists.

It’s also liberal poppycock that there aren’t smart conservatives or evangelicals. Richard Posner is a more-or-less conservative who is the most cited legal scholar of all time. With her experience and intellect, Condoleezza Rice would enhance any political science department. Francis Collins is an evangelical Christian and famed geneticist who has led the Human Genome Project and the National Institutes of Health. And if you’re saying that conservatives may be tolerable, but evangelical Christians aren’t — well, are you really saying you would have discriminated against the Rev. Martin Luther King Jr.?

Jonathan Haidt, a centrist social psychologist at New York University, cites data suggesting that the share of conservatives in academia has plunged, and he has started a website, Heterodox Academy, to champion ideological diversity on campuses.