I think normal balanced people are not that talkative in public forums.
It's us, the slightly broken ones (and the totally unhinged idiots and bigots and so on) that comment much on social media...
The first couple I can think of could be gamed or result in metric dysfunction.
- Using one's actual name AND photograph (to introduce some exposure and shame into the game)
- In-group ramifications for in-group bad behaviour
I can’t prove it, but it seems to me that a social network where the social graph is optimized for minimizing physical distance has more potential to encourage good behavior.
I’d also note this has been done successfully before, for example with non-denominational churches. Of course some basic shared religious beliefs help, but I’d argue that many/most of congregants who attend regularly are primarily motivated to do so by the social aspects.