The short answer is that you (https://news.ycombinator.com/newsguidelines.html).
For a longer answer, I need to clarify the principles we rely on. I'm happy to give that a try, as long as it's clear that I'm not commenting on the specific topic of this thread.
People are allowed to be wrong on Hacker News [2]. They have to be, because we're all more or less wrong about most things.
It's not that the truth doesn't matter—it matters enormously! But it's not the moderators' job to decide what is true vs. false. It's the community's job to hash that out through respectful discussion and debate. Mods couldn't do it even if we wanted to—we don't have a truth meter [3]. Plus the community wouldn't stand for it. There would be a huge backlash against the mods imposing their views on everyone else.
Wrongness is part of hashing out the truth. One needs to be free to visit wrong points in the solution space, or we'd all be trapped in a hell version of the old nine-dot puzzle (the one that spawned the phrase "thinking outside the box") with no solution.
"Spreading false propaganda" is, of course, an extreme case of wrongness, but the right scope for describing the principles here is wrongness-in-general, whether it's being wrong in an extreme way or just ordinary wrong-being.
It's true that posting in bad faith, e.g. saying wrong things despite knowing that they're wrong, is worse than just being mistaken. But can we decide who is and isn't doing this? That would require reading their mind and/or heart, and that's impossible—so we can't use that as a basis for moderation.
Internet readers are too quick to jump to the conclusion that someone else is posting in bad faith. Nearly always, the other person is as sincere as you are. It's just that their background is so different from yours that they've ended up holding an opposing view on a charged topic.
Most people find it hard to tolerate differences of opinion that are outside of a certain radius from their own position. We can call that the "comfort radius". In the past I've called it the "shill threshold" [4]. Past that radius or threshold, i.e. outside one's circle of comfort, it feels impossible that anyone could possibly hold such obviously-wrong views in good faith. The other person must be a shill, a propagandist, or worse. What other explanation could there be?
Well, here's the other explanation: that person has a background different enough from yours/mine/ours that entirely different things feel obvious to them. The world is much bigger and more diverse than your comfort radius, or mine, can easily allow for. If the delta between X's background and mine is big enough, X's views are going to feel not just wrong, but obviously and incredibly wrong, and—as the delta gets larger—appalling, barbaric, and so on.
So what should we do? We should assume good faith, because assuming bad faith is wrong far more often than it is right, and instead work on tolerating the distance between the other person's view and our own. By "tolerating the distance", I don't mean agreeing with them. I mean being willing to endure the discomfort and bad feeling in one's own system (the rage, fear, you name it) that comes up when encountering a view that feels obviously and incredibly wrong.
This is sometimes called "bearing the unpleasant manifestations of others" [5]. It is hard and takes practice. Actually, it's one of the hardest things we have to do, but also one of the most important. (I am not advertising this very attractively, but it does suck.)
To the extent we do it, a kind of metabolic process takes place where one's intense initial reactions get converted into a range where one becomes able to do what I described above: respond to false information with correct information, and to bad arguments with better arguments, while—I'll add one more thing—remaining in good-enough connection with each other.
Or to go back to short-answer mode: if you're hot under the collar, wait till you cool down before posting [6].
[1] https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...
[2] https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...
[3] https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...
[4] https://news.ycombinator.com/item?id=35932851
[5] https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...
[6] https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...