I agree with David Sirlin. Punishing players for using exploits is arbitrary, because the line between exploits and smart play is itself arbitrary. Is it wrong to find a safe spot from which you can kill monsters? Some might think you should not have that advantage. Others might say that weak AI is a fundamental aspect of games and taking advantage of its' stupidity was normal. Take it too far and players will be generally afraid of playing smart for fear of being banned for bug abuse.
I think rather than banning people for using exploits, it would be better to offer a large sum of real money to any player who told them about a serious game breaking bug and kept it quiet until it was patched.
I think rather than banning people for using exploits, it would be better to offer a large sum of real money to any player who told them about a serious game breaking bug and kept it quiet until it was patched.