a) You could say this about any communication channel- the web, email lists, in-person meetings. Should we require a moderator in every social sphere?

b) Personally I think butting heads and being outraged by what others are saying is the bigger factor in polarization, which this would actually help with (at least, I've noticed I became a lot more politically nuanced and a lot less emotional when I made a concerted effort to pare down my twitter feed using blocks and mutes)