> Downvotes will happen regardless of how well reasoned your argument is

Some will, but its very rare that I've seen posts retain a net of negative moderation when they contribute substantially, regardless of the side of an issue they are on (though I've seen controversial-but-substantial comments quickly get heavily downvoted before recovering.)

And I've seen this on every side of issues -- often to opposing posts in the same discussion -- so I don't think its an "echo-chamber" effect, but more that certain topics bringout more kneejerk negative responses from people on either side.

(Its funny that, in regard to accusations of HN being an echo chamber or hivemind, I've seen various posters proclaim with confidence that it was -- and that that hivemind was, variously, liberal, leftist, libertarian, capitalist, pro-corporate, anti-corporate, and in support or opposition to various companies, and any of a number of other things. I think people are way to quick to equate some people disagreeing with or downvoting their posts to HN being a hivemind biased against them.)

Bad threads produce bad behavior. By definition. When I see it happening, I flag the thread. Sometimes despite wishing that there could be a positive discussion of the subject because the subject is relevant and important and intellectually interesting.

I think "Maybe next time it comes up the comments won't devolve."

My unpopular opinions frequently get early downvotes, but it seems that it'll swing back into the black given enough time/eyeballs, if I've made a good argument.

Of particular note, sometimes expressing an unpopular opinion on a sensitive subject (or a subject on which some people have very strong feelings, even if it's not sensitive to most people) can trigger a cascade of "revenge downvotes". So while the original comment might get upvoted back to positive, comments on completely unrelated topics might pick up undeserved downvotes.

I once had a few week period where I noticed the majority of my comments drop by exactly 2 karma, usually around the same time of day, regardless of how many upvotes they'd received or how heavily trafficked the thread was. My best guess is that I'd upset two people (or one person with two accounts) and they kept clicking back on my profile until they got bored with it.