It's usually something they heard from equally idiotic celebrities like Sting, Madonna, Alec Baldwin or Charlie Sheen. A friend of mine recently expressed her disgust for evangelist Billy Graham. Whatever one thinks about religion, I can't see a logical reason why anyone would speak ill of Graham, so I asked why. She said the same thing about Newt Gingrich. It's not that these men stand for things she disagrees with, or that she has even looked into what they say.
Teachers fall prey to the college idiot phenomenon as well.
The teacher must have felt cool because many in the class laughed, but really, he's an idiot. It goes both ways. Some students find out their instructor's point of view and regurgitate it back to them like bird food. Instructor and student get a good laugh together, but no thinking is taking place. College idiots are especially infuriating because there's no arguing with someone who doesn't think.