"The only valid censorship of ideas is the right of people not to listen."
Tommy Smothers, American comedian/musician.
Often the result of a free, open, and honest exchange of ideas are better ideas than would happen were those individual ideas censored.
Not always but more than enough to make make widespread censorship a bad idea.
Take this blog as example.
I have the right to post my ideas while you have the right to decide whether or not you will read them.
Win/win and that's a pretty good idea!