Because censorship is a slippery slope.
While true, fear of censorship shouldn't get in the way of common sense. Maybe the new name caused a lot of people to forget that it's still curtisg behind that moniker; a kid that
on a regular basis either 1) threatens to 'hack' others, 2) tries to take credit any time some exploit is revealed, and 3) results to DDoS booters when his feelings are hurt. The name change was to try and get away from his reputation - and while he made a token attempt to change his ways, said attempt lasted for a week at best.
To turn that question on you, though... if we allow one, why not allow more? More and more malicious threads will start, and eventually they'll get their own subforum. Since there are many varieties of jackassery, the subforum will turn into an entire category of subforums... and so on.
HackForums (and several other similar communities) originally started with C|EH-centric goals. Whitehat, actual security discussion, etc. Kids like this turned it into the shithole it is today. I'm as much against censorship as anyone else - but I happen to like this place, and wouldn't want to see it end up the same way.