In this way, faculty are like columnists for major newspapers. Columnists for, say, the New York Times are perfectly free to write whatever they like (within appropriate professional guidelines, of course). But the range of opinion expressed in those columns is terribly narrow. The problem is not that the Times is exerting pressure on its columnists. The problem is that in order to be a columnist for the New York Times to begin with, you have to be the kind of person whose opinions already fall within a specific range. The same goes for faculty. Universities are generally pretty good about not exerting overt pressure on faculty and their research. Intellectual freedom is generally respected. But the university doesn't need to exert any pressure, because it's already filtered out the people who would need to be pressured. Those who survive are, for the most part, narrow specialists who care little about what's happening outside their own area of specialization.
When you critique the media and you say, look, here is what Anthony Lewis or somebody else is writing, they get very angry. They say, quite correctly, "nobody ever tells me what to write. I write anything I like. All this business about pressures and constraints is nonsense because I’m never under any pressure." Which is completely true, but the point is that they wouldn’t be there unless they had already demonstrated that nobody has to tell them what to write because they are going say the right thing. If they had started off at the Metro desk, or something, and had pursued the wrong kind of stories, they never would have made it to the positions where they can now say anything they like. The same is mostly true of university faculty in the more ideological disciplines. They have been through the socialization system.