How about if the 'auto-attack' feature is disabled after say... 5 minutes or less of inactivity (not moving your character around or something).
That way, you can prevent people from exploiting it without any noticeable changes to gameplay.
P.S. Here's a scenario, something that's bound to happen to me eventually:
I'm within aggro-range of a mob, but have to leave urgently. I remember the rules and so I log-off first. That's all fine. But then, later, I want to log-on again.
Now, for me, it takes 20+ minutes to log-on, and while doing so it takes up about 95% of my CPU's processing power, so I can't do anything else. Now, since I'm not brain-dead, I'm not exactly content to sit and stare at the loading screen for over 20 minutes, so I go off and do something, like get a snack.
Then, supposing the servers are running fast today and I log on in ten minutes, or maybe I get held-up in whatever I'm doing, and I don't realise the game has started running.
Since I'm in aggro-range now, I get attacked by the mob, and the infamous process begins.
I come back, expecting to find a loading screen with a full bar, but instead find I've been banned. "Oh no"
How could that be my fault?