Most importantly, we should understand the difference between censorship and filtering.
Censorship is an act of government that, by definition, precludes free choice.
The US constitution guarantees free speech, and thus restricts government censorship dramatically. Censorship at other times is a violation of our civil rights. Parents and teachers filter students and kids' exposure to all sorts of things all the time. We monitor their playmates and don't let them talk to strangers. We are encouraged to monitor and control what shows they watch on TV, the songs they listen to on the radio and the books they read.