The issue of intolerance for conservative and libertarian viewpoints on campus, raised by David's post below, is often discussed in terms of the harm to the students who suffer for expressing their views. The more serious problem, however, is the impact on the quality of discourse on campus for students of all ideologies.

It is true that the vast bulk of the retaliation faced by students who express locally unpopular right-of-center views on intolerant campuses is relatively minor - social ostracism, petty harassment by the administration, and so forth. Most of the people involved will suffer little if any lasting damage. However, many will choose to keep quiet if the price of expressing their views is petty harassment or ostracism.

We can, if we want to, criticize these people and argue that they should be willing to take more risks. The practical reality, however, is that many (perhaps most) people care more about their social standing and about avoiding even minor harassment than they do about expressing their views on political issues. The predominantly leftist schools I attended were, on the whole, far more tolerant and open than 1980s Brandeis was, as David describes it. I usually said what I thought and didn't worry too much about the consequences (some of my classmates would say that I worried too little:)). Even so, I knew quite a few conservative (and even some moderate) students who kept their views to themselves for fear of hostile reaction.

The result may be a campus environment where debates about controversial issues such as abortion, race, or other matters will be one-sided because most of the adherents of the opposing view are keeping quiet. This reduces the quality of debate (and education) for all students, including those who adhere to the dominant view. The point applies to the expression of left-wing views at intolerant conservative institutions as much as the reverse. It just so happens that we have far more predominantly left of center schools than right of center ones. Thus, there is good reason to worry about political intolerance on campus even if we don't care much about the hurt feelings of conservative or libertarian students.

UPDATE: Some of those who claim that campus intolerance of conservatives and libertarians is not a significant problem argue that right of center students are themselves obnoxious, intolerant, and so forth. If there really is an overrepresentation of such people among outspoken campus right-wingers, this fact may itself be the result of PC intolerance. If speaking out in favor of un-PC viewpoints can lead to social ostracism, an obnoxious jerk is less likely to be deterred by this danger than a conservative who is generally nice and popular. After all, the jerk is probably already widely disliked, while his more popular counterpart has much more to lose from any PC backlash to his remarks.