if he just made an account from a different IP, what makes you think he won't just rejoin, under a different name ?
If he does and I don't notice, then that means he's readjusted his attitude and it's not that bad a thing -- if Fobos is verified as the new account holder though, of course I'll ban it immediately, whether the new account has been good or bad, as it's a ban-dodge.
Isn't that a little counter-productive? I mean, the only thing banning his new account would accomplish is it would make him dodge the ban again. It's a vicious cycle, and there's no real reason for it either if he's adjusted his attitude. It all comes down to what you think the purpose of forum rules is. Punish people for wanting to be a part of the community or keep the peace? I'd say it's the latter, and if he's not disturbing the peace there's no reason to punish him further.
To clarify, it's a matter of the time frame. I had somebody dodge a ban two years later and I didn't care. If Fobos comes back in a couple of days, is good for a week, but it comes up that it's a ban-dodge, then I'll ban him again, because the act of ban dodging itself shows that he hasn't really learned and will likely misbehave again. A polite email after a month would be a superior method of getting back on the boards. I don't want to encourage mute dodging as a game or muting is pointless. And no, the cycle doesn't seem to go on forever -- people get tired and most of them don't know how to pretend to occupy the entire IP range. If I run into a problem like that, I don't have a solution, but it isn't a problem that plagues any forum I've been to.
I don't think your question is fair, in that those aren't my only choices. Keeping the peace is not the only reason for forum rules, and I'm not just doing this to "punish people who want to belong". I don't care if Fobos wants to belong, because he's an unrepentant asshole who wasted my time harassing other people who are genuinely interested in what's going on here and who express that in a non-destructive way. This is why he is being punished.
If there's a hypothetical Fobos who has behaved for a few days, then he's still gone, because I can't give him second chances forever. Fobos has been good for a few days before. Having people like him around chases people away, people that I'd much rather have around than Fobos. Choosing between them is simple. I can't have them both if Fobos isn't willing to change.