Censorship is based on the idea that Evil is stronger than Good.
Censorship says "Go ahead - educate your children in morals and ethics, by word and deed. Set a good example. Read to them nightly from the Bible. It won't make a fig of difference because the moment they see one nasty picture, hear one racy lyric, or read one piece of perverse prose, they'll be corrupted. One exposure, and they'll spend the rest of their lives toking and looking for cheap sex."
Of course, the forces of censorship never say this to your face. Not directly. But if you listen to their arguments with the above in mind, the message comes through.
The second message that comes through is that they're better than you. THEY can remain pure after seeing those EEEVIL pictures, but YOU and YOUR KIDS can't. You're weak.