I get that this would mean more if the user in question was a jerk or was annoying in a way, but Kahnu is legitimately trolling most of the time. I can't fathom a reason why you would want to keep him around
I mean if you do that then you'll have hundreds of bans. Plus, it's not sensible. If I started stuffposting on the forums, then why would I be banned if nothing was happening in the game? You shouldn't be banned for previously doing things (some exceptions). I would think that you wouldn't immediately punish them, but just be less lenient with them. If they screw up, they're screwed.
I feel like Kahnu gets stuff on a lot more warranted. I'm not denying that he has been an idiot and an ass, because he really has, but still he gets a lot more stuff than people who do worse things.