“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.”

We progressives believe in diversity, and we want women, blacks, Latinos, gays and Muslims at the table — er, so long as they aren’t conservatives.

Universities are the bedrock of progressive values, but the one kind of diversity that universities disregard is ideological and religious. We’re fine with people who don’t look like us, as long as they think like us.

O.K., that’s a little harsh. But consider George Yancey, a sociologist who is black and evangelical.

“Outside of academia I faced more problems as a black,” he told me. “But inside academia I face more problems as a Christian, and it is not even close.”

I’ve been thinking about this because on Facebook recently I wondered aloud whether universities stigmatize conservatives and undermine intellectual diversity. The scornful reaction from my fellow liberals proved the point.

“Much of the ‘conservative’ worldview consists of ideas that are known empirically to be false,” said Carmi.

“The truth has a liberal slant,” wrote Michelle.

“Why stop there?” asked Steven. “How about we make faculties more diverse by hiring idiots?”

To me, the conversation illuminated primarily liberal arrogance — the implication that conservatives don’t have anything significant to add to the discussion. My Facebook followers have incredible compassion for war victims in South Sudan, for kids who have been trafficked, even for abused chickens, but no obvious empathy for conservative scholars facing discrimination.

The stakes involve not just fairness to conservatives or evangelical Christians, not just whether progressives will be true to their own values, not just the benefits that come from diversity (and diversity of thought is arguably among the most important kinds), but also the quality of education itself. When perspectives are unrepresented in discussions, when some kinds of thinkers aren’t at the table, classrooms become echo chambers rather than sounding boards — and we all lose.

Four studies found that the proportion of professors in the humanities who are Republicans ranges between 6 and 11 percent, and in the social sciences between 7 and 9 percent.

Conservatives can be spotted in the sciences and in economics, but they are virtually an endangered species in fields like anthropology, sociology, history and literature. One study found that only 2 percent of English professors are Republicans (although a large share are independents).

In contrast, some 18 percent of social scientists say they are Marxist. So it’s easier to find a Marxist in some disciplines than a Republican.

The scarcity of conservatives seems driven in part by discrimination. One peer-reviewed study found that one-third of social psychologists admitted that if choosing between two equally qualified job candidates, they would be inclined to discriminate against the more conservative candidate.

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