Listen to El Presidente or be arrested - Students at Ohio State University planned to protest a Bush speech by standing up and turning their backs. But they didn't go through with it. Why? Because they were threatened with arrest and expulsion if they did. See: OSU quells Bush protest but still gets angry words

This part sums it up:

"The purpose of allowing the president to speak in our system is to allow him to convey his views," Vasvari [legal director of the American Civil Liberties Union-Ohio] said. "He should not be ensured or expected to have an enthusiastic audience. Acting in that way is no better than those who round up cheering crowds to line Saddam Hussein's motorcade route."