It's been a while but I don't recall a ton of politics on the usenet groups I used to participate in (mostly tech subjects). Of course there were groups for politics, and sometimes a thread would go off on a tangent, but the nice thing about usenet is it was easy to killfile people or threads that you didn't want to read anymore.

When I used it it seemed like it was mostly real names (.edu accounts) at least on the groups I read, so maybe that kept people in check a bit. Though that would have been easy to spoof I'm sure.

My department also had some local groups that did not propagate. So it must be possible to stand up your own NNTP server and have groups for your local users that are at least in that sense "private"