"One reply per post."

I'd say:

- Using one's actual name AND photograph (to introduce some exposure and shame into the game)

- In-group ramifications for in-group bad behaviour

Facebook is a pretty good example of how neither of those things actually help, and if anything only amplify the harm that comes to marginalized people who have good reasons to not use their real names or faces.

I wonder if that’s due to everyone ending up in bubbles on FB.

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.