I (and others) have made it an explicit goal to try and maintain civility and to focus on things that are immediately useful to tech practitioners. It's
amazing the amount of shit that gets cut out when you don't normalize the mindless upvoting of news, marketing, and politics.
The closest we've come in recent memory was a long grumping in a subthread about ESR in a submission involving Rust vs. Go.
The basic problem is just that there are a lot of people who want to inject politics into everything--and that's fine, and frankly even correct--but they don't realize that by doing so they destroy the safe space for civil technical discussion, of which there are few these days.
Some of the things that keep the discussions civil (in my estimation):
1. Public moderation logs, none of the secret cabal stuff that goes on here. Thus, users never have a clear ground to say "help help I'm being repressed!". Towards that end, at least one user banned multiple times here has been a reasonably civil member of our community--though we do try to keep him from getting to longwinded about certain topics.
2. People have multiple reasons to select why they're flagging something, and downvoting something just because you disagree with it is actively discouraged. Allowing people to get used to knee-jerk downvotes has made HN nastier, and it's something you can't really walk back.
3. We have a clear tag system for organizing submissions, and a general policy of pointing out things that don't fit (and adding tags for new things). In this way, we get to ignore the brunt of articles--news, marketing spam, other bollocks--that would have to show up and be flagged away manually by the userbase. In effect, it seems people submit things with a little more care and submit things that are actually in the wheelhouse of the community.
4. People are not afraid to point out when community norms are being broken, and are not afraid to use the mechanisms in place (meta threads, tag discussion threads, PMing) to fix those norms when they aren't working correctly.
5. Invites are handled through the existing userbase, and we are all aware that we are somewhat responsible for who we bring in. In some small way, everybody feels directly responsible for the community and how it evolves--and they often put some minimum effort into vetting the people instead of just opening the floodgates to normies and marketers (for lack of a friendlier term).
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I guess the other thing that helps is that, in general, we've had open discussion about the role of politics in the site, and the general population seems to recognize that, while some discussion is to be encouraged (and cultivated in places like our `culture` tags), we don't want to just start indiscriminately hosting submissions and their resulting arguments. Some, like me, would prefer that those submissions never appear. Others would be happy to submit politics all the time. The community though, in agggregate, is empowered enough and--for now--wise enough to strike a balance between those two extremes.
It's a good place, and I hope we don't fuck it up too soon.