As far as I can tell this dynamic has nothing to do with reality. Reality is that the HN community has millions of people, is diverse in many ways including internationally, and is divided on divisive topics. That is already enough to explain the comments that show up. But none of us is wired for dealing with that. We're wired for loyalty to our tribe, needing to feel safe, and suspecting outsiders.
It's painful to encounter a sharp opposing view, and people are angrily sharp on divisive topics. Reframing the other as a foreign spy or whatever insulates you from that. It relieves you from considering what truth there might be in that view, and reinforces loyalty to your own—at the cost of feeling surrounded by infiltrators and enemies. This is poisonous to thoughtful discussion, which depends on people being willing to open to differences and truths they may not yet see.
Since the actual phenomenon is vanishingly rare compared to the insinuations people make about it, we have a rule that users not post such insinuations without evidence. A feeling is not evidence. Even the sense "there are a lot of green accounts saying things I disagree with" is usually just a feeling, because we notice things we dislike more vividly than we notice anything else [1]. People on the opposite side have the opposite perceptions, but the identical feelings.
Notice how when people post claims about astroturfing, trolls, and spies on HN, they don't include links; just as when they make claims about "threads about $topic", they don't include links. Why is this? If the perception were of reality rather than a feeling, specific examples would always be available, yet in practice they almost never are. The discussion falls apart when specific cases are mentioned because (a) people never agree about those, and (b) such data as there is never supports the claim. The discussion always stays in a mist of generality, breeding bacteria of suspicion.
[1] Does anybody know or have a name for this bias? It's a huge factor in these discussions and it needs a good name.
I agree that these are probably exceedingly rare on HN, but it seems technically implausible that you'd be able to accurately identify them.
Second, some of the analysis can be done by anyone who wants to. When you encounter specific claims of astroturfing or shillage, look at the history of the commenter being accused. Most of the time their track record makes it implausible. If someone has been posting to HN for five years including about, say, garbage collection in Julia, what are the odds that they're secretly a foreign agent? Far lower than that the other user tossed off an accusation without pausing to look. It's usually not even a serious question.
Now consider that these demonstrably low-probability cases are exactly like the rest of the accusations people post here, and one has evidence for a common mechanism underlying the entire class. I don't assert (how could I) that there are no cases of genuine manipulation that fall outside it. But after looking at thousands of such claims, I believe that this and similar tests account for nearly all of them.
(Edit: it's different in cases of startups or projects trying to game HN to promote themselves; that's super common. And more sophisticated corporate astroturfing is something we've occasionally run into. But on these political, national, and ideological issues: zilch.)
"Oh no, now all the coordinated disinformation campaigns will start posting five years of high-quality good-faith technical discussion on a variety of topics to evade your heuristic" /s
Uh, confirmation bias? Your description is a bit off, it's not that "we notice things we disagree with", but that we notice things that confirms our previous beliefs, in this case that green accounts post opinions that you think come from spies or astroturfers.