When I see that sort of thing, this is what I imagine. [http://www.youtube.com/watch?v=o7WSgC9oGic&t=1m55s]
I kind of second Topaz, as well as a few others. It accomplishes nothing, makes you look like a fervent manchild, and doesn't actually address any problem at all. However, there is one thing I don't agree with...
Te site should not ban them. Just put a tag on their profile stating that they had requested to be banned, again, like a child. Anyone can see this tag but the poster. That way, when they inevitably return to school, we can all see it and laugh at them.