Todd, you fuck, did you ever play on a MUD where the gloves were off and the admin only stepped in for actual coding/bug issues? People can be good, yes, but online, they can also be astonishingly bad.
And the problem is, because of the nature of... well...
games, generally, you can never actually compel players otherwise. Players who want to be assholes generally have
nothing to lose. They laugh at any attempt to control their behavior. You can't even effectively ban them, generally - if your game is F2P, they just roll another account. If your game requires a purchase, that might slow them down a bit, but it's surprisingly not as effective as you might think in actually stopping them.
And if anything, they tend to be better at manipulating the system than you are... If your game has consensual PVP, they'll know every trick to force you to "accidentally" consent to PVP. If you have always-active PVP, but some sort of anti-griefing enforcement, they'll know how to get *you* to be marked as the griefer instead of them. If you have NPCs that try to guard cities, they'll know how to make the guards target you instead of them. It goes on and on.
And even if, after all that, you manage to ban one, and he stays banned? You've still "lost". He got exactly what he wanted, ultimately - he made you mad, caused you problems, and wasted your time.