Historically, we have tended to take the view that trying to squelch a troll (say) by locking the account doesn't work, for the simple reason that the human behind the account can always simply create another one. If we've got a person exhibiting problematic behavior, it would be better to have it all in one box rather than several. It's the classic game of internet whack-a-mole. Some more modern social networking systems illustrate the problem grandly.