I know I'm a bit late to this party, but frankly I think this argument is ridiculous.
It will not be a problem, especially with an opt in/out system. I have yet to see a gm evil enough to lock someone out for no reason, or even without plenty of warnings. If a gm wants to micromanage their rp, let them. If they want to be a troll to someone, which I truly don't understand why you think will be so common, let them - the mods can deal with it, and I guarantee it won't happen often enough to be a problem.
Perhaps an appeal system would work? If a gm doesn't provide any reason at all, a player can hit an appeal button, immediately overriding his blacklisting and alerting the mods to check it out. It'd have a large warning stating that to abuse this will be punished severely. The mods then check it out (perhaps put a field for the gm to state a reason (required) before being allowed for both the player and mods' benefit) and decide who is at fault. Either way it is blatant trolling, and can be punished as such (especially for the player if they appeal just for the luls). Perhaps even limit how many appeals one may have for life? Say, 3?
Lastly, restricting the ability to post cannot be compared to deletion of content. Allowing any person to delete someone's hard work is evil. Allowing someone to police their own "territory" to keep order and/or be a dictatorial idiot (and be punished as such) is a great idea. Removing someone won't happen often to begin with, and when it does I am very confident the reasoning will have been discussed beforehand (and warnings probably delivered as such). But as said above, perhaps it is best to just let Mahz decide himself, since we clearly won't be able to agree?