But then the next day a different post on the same topic could have an entirely opposite hivemind, often no discernible reason.
I'm not so sure this is a huge effect. I often express "incorrect opinions", and get some amount of downvoting or ridicule, but not usually to a significant degree. When I've had my comments dogpiled, I can see that it happened because of how I stated my opinion more than because of the opinion itself.
Sometimes the same story will be flag killed one day, front page the next.
Look in a thread where China is mentioned and you'll see the real face of many HN'ers - if they aren't removed before you see it. Luckily the MOD'ing is pretty good.
Unfortunately since most people aren’t experts on most things, this turns into a bunch of fugazi. People who are financially or academically successful in business or engineering or marketing think they understand politics too.
This is what happens with topics like China. I don’t care about China much. So I end up defending it because the negativity towards it by the Global North is staggeringly inconsistent.
HN is actually one of the most homogeneous public communities I've seen.
And judging by how few downmodded posts are around, self censoring.