Thinking about past professors, it strikes me that two of my three betes noire in that department would either tell stories about past students who claimed that they had ruined their career, or explicitly state that they'd almost certainly be called for a reference, and explicitly say that if people didn't play along, they wouldn't have a career. (Both were at state universities.) The thing is, most of these experiences were actually in the classroom, during seminars that they were being paid (sometimes quite handsomely) to teach, and as I think about it now, I can't fathom how the subject might have come up.
(The third bete that happened to be noire was in conservatory, and probably judged (correctly) that we wouldn't have let her get away with that.)
I recall JK Galbraith's musing on the universities of India, when he was travelling with JFK -- they struck him as being like the American state universities: either play along with things or find yourself back working the fields. Hardly a fringe figure.