The only form of censorship I truly support, is that of short-term censorship of military matters (particularly of actions currently underway, re: war) when revealing that information could jeopardize the success and the lives of those involved. Unfortunately, this inherently creates an arbitrary gray area about what defines “national security” and “state secrets”, and opens up the potential for abuse. Howvever, I think this is a necessary evil, and one that’s better to err on the side of safety than potentially destroy yourself for the sake of a news scoop.
I don’t consider libel laws to be a form of censorship: they’re not limiting what people can say, they simply force people to be accountable for it if it’s damaging and (this is the important part) truly groundless. You can say any cripplingly devastating thing you want about someone if it’s true, or if you had substantial reason to think its true. Interestingly enough, you can tell all sorts of lies about someone if it makes them sound good (hey, politics!)
Porn (kiddy, animal, or otherwise), violence, language, Huck Finn, Mein Kampf, whatever. I see no reason to try to stamp it out. I feel it’s better to let people decide for themselves what they’re “prepared” for, and trying to deny or hide something you don’t like isn’t going to make it go away. Learn to deal with it, and the problem will be solved much better than censoring it ever would.
I’m not a big fan of “protecting the children”, for that reason. You can shelter your spawnlings all you want, but the “ugly” facts of life are going to come out sooner or later. IMNSHO, it’s better to deal with it sooner than later, rather than let them build up a false world view that will inevitably be shattered. Don’t bury a field of psychological landmines in the naieve hope of “protection”.