I just have one little request: I think that when these guys are banned, we need to see more cute little tags under their names (Idiot, too stupid to live, etc etc…)
Maybe easy in the short run, but damaging and far from relaxing in the long run. This place is dedicated to Stomping Out Ignorance, and that doesn’t encompass easy censorship. The folks around here are bright and opinonated, so maybe–just maybe–closing and leaving the threads provides documentation for actions taken.
View and decide on your own.
Veb
The Straight Dope Protest was started by a troll that got banned, but the thread went on to make Threadspotting due to the subsequent hijacking.
And Homer’s monkey butler thread was closed to save him further embarassment, but the OP is still a favorite of many of the posters and linked to often, even though the thread has only 6 replies.
I’m sure there’s other examples out there if you look.
You know, Homer REALLY lives up to his username…
Well, I do my best. 
–Tim
Leaving aside such threads that the SD Protest and the Monkey Butler, there’s a damned good reason to keep closed threads around. As Veb states - they’re proof of what happened.
If a troll’s thread is closed, when he inevitably bitches about it (Probably under a new name), the mod who closed it can link to it, and the board can see why, and make our own decisions.
If, however the thread is deleted, when the troll inevitably bitches about that, it’s their word against the Mods’. Chances are, the Mods’ll be in the right, but if the thread’s gone, the only ones with proof are the ones who read it before it died. The person whose thread was deleted could, conceivably paint himself as a victim, and actually get support, whether he was right or not.
Let me just say that “Monkey Butler” is the funniest thing I’ve read in a long time, and I’ve been following the JDT threads…