There is still yet to be an administrator\moderator response here. However, I think the difference is fairly simple.

This is a public message board, so telling someone to "shut up" is denying their right of posting their thoughts - which is the whole point of a message board.

The Anti-Xion and other such topics are (probably) not meant very seriously. And as Xion noted here, he is not really offended by them. If he is in fact offended, he should notify an administrator or moderator and they will act accordingly to close the topic(s).