I think this is one of those things that only ever makes sense in the abstract. How would this rule apply to Stratton Oakmont v. Prodigy? Would it make sense to tell Prodigy that they'll be immune from defamation suits if only they agree to make their offensive language monitoring opt-in and publish a new code of conduct permitting racial slurs?
I'm honestly not sure... it could also backfire with intentional social groups... such as someone created a social network expressly for progressives or conservatives, where repeated contrarian rhetoric is simply disallowed (for good or bad), for people who want to live in their bubbles, like MSNow.
(last comment regarding MS Now is meant for humor)