The way I see it, he's abusing a service provided by Nimrod, so it's perfectly fine for Nimrod to take away his privilege (since that's what it is) to use it. If the only way to do that is by a complete IP ban, so be it. I can see where the reservations to such actions come from, and I suppose they could be addressed by coming up with some sort of formal process of reaching a verdict about banning or not, but I don't think the whole list server enterprise is big enough to warrant such an institution.

I don't know whether it's possible, but some sort of server spam prevention (like max 3 servers per IP or something) would be nice to avoid such problems in the future, perhaps?