"Please don't post insinuations about astroturfing, shilling, bots, brigading, foreign agents and the like. It degrades discussion and is usually mistaken. If you're worried about abuse, email hn@ycombinator.com and we'll look at the data."
https://news.ycombinator.com/newsguidelines.html
https://hn.algolia.com/?sort=byDate&dateRange=all&type=comme...
The reason is that internet users are overwhelmingly too quick to accuse other people of being spies, manipulators, etc.—it's a garden-variety form of online disagreeing that is at least as destructive to the community as anything people are accusing each other of doing.
We have long years of experience investigating this stuff and have nearly always found that it is simply a disagreement between people with different backgrounds happening to have different views. That doesn't mean there's no organized abuse—just that (as far as we can tell from the data we have) that's a rarer phenomenon than internet users poisoning the ecosystem unprompted. This leads to ugly things like mob behavior and good-faith users being hounded off the site. That's absolutely not ok, so we have to be careful about enforcing this rule.
For past explanation, if anyone wants more, see for example https://news.ycombinator.com/item?id=27398725. I also made a list of past moderation comments on this at https://news.ycombinator.com/chinamod.