I think HN's moderation has problems with certain topics that have mysteriously become high-voltage in certain social circles, like Damore/men's rights/etc. But crucially, no worse than other general purpose discussion sites and mostly it's still better. You can show dead, view flagged stories etc. The problem is comments that trigger Valley liberals tend to be criticised by the mods on the grounds that other people would respond badly to them, which is annoying, because it's actually those who respond badly that should be given a finger-wag, you'd imagine.
But still that's a far cry from banning politics, which HN doesn't do, and it doesn't even ban discussions on those hot topics, they're just much more likely to be flagged by users. I read HN with showdead turned on and by starting at the (oddly hidden) /active URL, which shows flagged stories, so I have a pretty good sense of how much stuff gets flagged and why. It's a mix of things and not entirely easy to predict. It's not politically biased in exclusively one direction either. To some extent what gets whacked seems to depend on what time it gets posted, ditto for comments. Try criticising the EU on any HN thread during the European daytime and lots of outraged Europhiles will vote you down to -2. Then when the Americans wake up and the "EUropeans" go to bed, the same post will get positively re-rated. It's clearly a matter of voter identity and not the wording of the posts themselves that are the issue.
I used to love Slashdot's style of user-driven moderation. It did require people to pick adjectives to justify their mod decisions, and then the meta-mod process helped weed out abusers. It's a pity it never caught on outside that site. HN's approach is very different, and some days I think it's worse, other days I think it's better. I'm not sure Slashdot had to deal with the same kind of political problems we have today though. Perhaps the closest was open source vs Microsoft, or something like that. I don't recall the same kind of extremist social positions that burn so much bandwidth on all discussion platforms (that don't ban them).