I don't know if the limit needs to be geographical. I'd think it could be segmented by interest, ala discussion forums for particular hobbies. Those are private

I don't know if the limit needs to be geographical. I'd think it could be segmented by interest, ala discussion forums for particular hobbies. Those are private and heavily moderated, there are 'village elders' (mods/heavily active users), people are on good behavior because of this, they always seem to have a section for more controversial/political discussions for those who want it - and they tend to be civil, surprisingly enough, because users have a rep to protect in the more generalized sections and don't want to be a bad citizen. And nothing is indexed by search engines, you have to go to the site and search. Reddit has this a bit with subreddits but it's far more loose and indexed by search engines, which I think is why it is problematic in certain ways.