Your comment presupposes all propaganda is negative, underhanded, corrupting; it is not. Propaganda is any propagation of doctrines, theories, or causes. For example, HN is a propaganda machine for start-up companies, people hoping to get rich quick, bleeding edge technologies, privacy advocates, the never-ending addiction to banal tech companies and their meaningless products, etc. Other things are propaganda too, like stories about gender equality, climate science, and "considered harmful is considered harmful". You can't try to convince people to act or think a certain way without the propaganda to do it. Propaganda is, by definition, genuinely held positions; just not always
your positions. The concept of propaganda is amoral, even if its subject matter is often highly moral.
Based on your examples, what you're really concerned about is morality and rules. What are the moral values of HN, and what rules should be imposed to enforce them? What morals are ok, and what aren't, by which people?
> Identifying oppressors is difficult but identifying the values of oppressors is easier.
Well, let's examine that. On the one hand, you probably disagree with the Chinese Communist Party using this site to try to gain sympathy for its doctrine. On the other hand, you might think it's OK for millennial Americans (who for whatever reason have culturally decided that capitalism sucks, and that some form of ism is the only alternative, if perhaps half-jokingly) to share articles with a similar message. They both may preach communism, or denounce capitalism. Which is OK, and why?
Basically, you want to know where the red line is. And that's the problem with moderation: there is no red line. There's a whole lot of blurred colors. You start with a very sensible, good, popular moral position like "no racism or sexism", and then you end up fighting weird angry splinter groups who have decent arguments about what it means to be racist or sexist; maybe you would be to them, or maybe they are to you, but neither of you believe you yourselves are. (Try to explain to the average nerdy fan of The Big Bang Theory that it's probably the most toxically misogynistic show on television, and you might find a heated argument; but is TBBT banned from HN?)
The only easy solution is to make a site which is literally dedicated to the morality of a single person - an autocracy. The rules are whatever that person says they are. But since some people don't like that idea (!) what you end up with is a benevolent oligarchy. A few people run things and try to be nice to the users, but basically it's those few people whose morals and values become the de facto rules. Those rules are intentionally fluid and based on interpretation and guidelines, to encourage as many users to use the site as possible, yet provide enough of a LART to keep Eternal September at bay.
The end result is that there aren't any definitive morals running the ship, by design. Go look - there is no explicit rule against sexism or racism. That would be too easy to argue. The vagaries of human morality are too loose, so you can't just eliminate what seems simple. You can only plumb the depths, interpret what feels bad, and chip away at it.