Universities are hothouses for ideas, a lot of them bad. Fortunately, most die a rapid death from mockery. But the trending campus admonishment to "check your privilege" is actually a good one.

The phrase is a left-wing way of winning an argument with your roommate without logic or evidence. It means that you're privileged -- because you're white, you're a man, or whatever -- and therefore you're wrong. It takes guilt by association to a new level.

The curious thing is that universities are dominated by the left. Surveys show most departments have few, if any, conservatives. And the people making the admissions decisions are drawn from the same pool. Privilege at U.S. universities isn't granted from the right.

But if you want to argue with your roommate, you have to be in the room. So who's privileged to be at an elite university? Well, men. Top schools try to admit an even mix of men and women, but if grades were the only criterion, women would dominate. As the (female) dean of admissions at Kenyon College wrote in 2006, men with good grades are "more valued applicants" because they're rarer.

Who else is privileged? Beneficiaries of affirmative action. After California banned the state's use of racial preferences in 1996, African-American and Hispanic enrollments at flagship universities fell, while Asian-American enrollments grew. Just as women lose out unfairly to men, the victim of one minority's privilege is often another minority.

Other beneficiaries of privilege? Foreign students. In theory, universities like foreign students because it makes them look multicultural. Actually, universities like foreign students because they pay the bills. According to Princeton, only six colleges offer full-need financial aid to foreign students.

And then there's the biggest privilege of all: having a stable family that values education. For a decade, I was privileged -- genuinely privileged -- to teach at Yale. I didn't ask all my students, but a common factor stood out among my advisees: They had married parents with professional backgrounds.

It's easy to say this is the kind of privilege that brings money. In some cases, that's true. But it's mostly about having parents who lead by example when it comes to learning, and who en sure their kids play the admissions game. Low test scores? That's what Kaplan is for. Are you boring? Liven up that application with summer camps!

Universities should stop trying to admit Peter by robbing privilege from Pauline. If even more women deserve admission than men, admit more women. If Asian-Americans outperform, admit them. But it's the left that runs the system, and it's the children of the professional class who benefit the most from it. And like their kids, that class is mostly liberal.

The irony is that you don't have to go to a top college to succeed. But it bothers me that those schools are building a self-perpetuating elite. Ivy League admissions could, after all, be by lottery, with every U.S. valedictorian given a ticket. That system would likely bring more diversity and be less easy to game than the current one, because it would simply reward individual achievement in the classroom.

So, sure, check that privilege. But not all privilege is bad. If all students had the kind of privilege that comes from a stable family, we'd be better off: That's a real privilege, and we have far too little of it. As it is, too much privilege in colleges today comes from a system biased toward those who understand it, and from treating students not as individuals, but as representatives of groups. And as the faddish popularity of "check your privilege" implies, that's the way the left likes it.

 - Ted R. Bromund is senior research analyst in The Heritage Foundation's Margaret Thatcher Center for Freedom.