Too often, American college students face a one-question test, based not on facts, but on ideology. The test: "Are you a liberal, or conservative?"

The correct answer is, "I'm a liberal, and proud of it."

That concerns me, but I'm not worried much about the students who get it wrong. I'm worried about those who get it right.

The young people that our educational system is failing are the students on the Left. We promise to educate them, but they aren't being challenged, and don't learn to think.

I was Chair of Political Science at Duke for ten years. At a meeting of department heads, we heard from the chair of one our Departments of Indignation Studies. "I find that I don't really need to spend much time with the liberal students," he said, "because they already have it right. I spend most of my time arguing with the conservative students. That's how I spend my time in class."

This woman was teaching conservative students how to think about arguments and evidence; how to make your arguments in a persuasive way. She was educating them. Her liberal students? They were given that one-question test, and practically no further instruction after that.

It may have come as a shock to the parents of these liberal students that they had learned everything they needed to know in high school. Having memorized a kind of secular leftist catechism, they were merely paying tuition so they could wander around the quads of Duke and enjoy themselves.

John Stuart Mill once argued that we should regard our overall approach to education as collision with error. He wrote: "[The] peculiar evil of silencing the expression of an opinion is, that it is robbing the human race; posterity as well as the existing generation; those who dissent from the opinion, still more than those who hold it. If the opinion is right, they are deprived of the opportunity of exchanging error for truth: if wrong, they lose, what is almost as great a benefit, the clearer perception and livelier impression of truth, produced by its collision with error."

The absence of dissenting voices in many departments is harmful, not so much to those who would agree with the dissenting voice, but those who are thus denied the chance to collide with error.

It's as if we asked students to play chess, but only taught them one-move openings. They think that pawn to king four is a better move than pawn to king's rook four, but that's simply a matter of faith.

Conservative students, by contrast, must learn to play chess as they encounter pervasive campus liberalism. They must study the whole game, not just the first move. They learn countermoves, they consider the advantages of different approaches. They have to defend their ideas by searching out empirical arguments, by reading articles and white papers.

"He who knows only his own side of the case," Mill wrote, "knows little of that.…if he is equally unable to refute the reasons on the opposite side; if he does not so much as know what they are, he has no ground for preferring either opinion."

Students who pass the one-question test find themselves in this position, and no one loves them enough to tell them. They respond to others' ideas and arguments with anti-intellectual, argument-stopping cliches such as "micro-aggression" and "check your privilege." They impugn the motives of their interlocutors ("you must be funded by the Koch brothers") or even impugn entire disciplines ("economists don't understand the real world"). This is turning academia into a toxic retention pond with a dangerous concentration of ignorance and ideological bigotry. And it is now gradually bleeding its way into mainstream culture.

This is not about liberalism – it is about education. Conservatives who don't understand liberal arguments are just as brain dead as today's most closed-minded liberal graduates. It's just that most conservatives can't make it through college without heavy exposure to opposing views.

Education requires collision with error. And many students of all ideological persuasions — but especially those on the Left — may finally begn seeing through a system would rather patronize than educate them.

Students should strive to hear the best arguments from the other side, and professors should facilitate such exposure. It's more interesting to play against the first team, and the victory (if it ends that way) is more worthwhile.

A young person's mind, once stretched by a new idea, never shrinks back to its original dimension.

Michael Munger is professor at Duke University and the former chairman of its political science department. Thinking of submitting an op-ed to the Washington Examiner? Be sure to read our guidelines on submissions for editorials, available at this link.