Anthropologists tell us that one window into a society is what is and is not taboo in that society. It’s interesting to look at America’s elite universities in this context. Let’s take examples of people and ideas that are not taboo, just from things that I’ve blogged about:
Being an unrepentant domestic terrorist, so long as you are an unrepentant leftist domestic terrorist; klansmen and neo-Nazis need not apply.
Suggesting that American Jewish leaders resemble stereotypes out of Der Sturmer, at least if you are doing so in service of a general leftist, anti-Israel ideology. (Pat Robertson or Pat Buchanan would get no “pass” if they made similar remarks.)
[Note: Ayers, Churchill, and Finkelstein, the examples provided above, don't teach at elite universities, but they have plenty of defenders and apologists at such universities, and none would be considered generally "taboo" as a speaker.]
Suggesting that any Jew with traditional religious values is unfit to serve in government, that a top-ranking Jewish U.S. official was more loyal to Israel than to the U.S., and that “right-wing” American Jews somehow pushed the U.S. into the Iraq War. Again, at least if this is in the service of hostility to Israel.
Being a convicted cop-killer on death row, with strong evidence of guilt.
By contrast, writing a private email concluding that one thinks that the science regarding racial differences in intelligence is uncertain is taboo.
One can have a lively discussion regarding whether some or all of these things are should be taboo, but the interesting thing is that the individuals who are most committed to keeping the latter topic taboo tend to be the same people who complain when others suggest that the former examples should be taboo.
In short, what’s taboo on elite American campuses is ideas and actions that many people find offensive, but only if those ideas and actions happen to conflict with the felt commitments of left-wing ideology.