Good points here. It's given me quite a bit to think of.
Let's define censorship as the suppression of speech, ideas, communication, and information in general.
Some people would say censorship is done by an authority. Let's define authority as a unit of administrative power and control. This is dang. This is also the group of people who have the power of downvotes. It's not the majority. But even if it were the majority (e.g. reddit), it doesn't matter. There's a bias. There is always a bias, whether it's HN, FB, reddit, X, Threads, Mastodon, Discord - all these websites are self-selective by design.
Authority (e.g dang/YC) builds a system (e.g. downvotes) to destroy bad content. As dang puts it, they're white blood cells.
But back to censorship. Censorship is the suppression of communication. If something hits -4 downvotes, it is hidden unless you have showdead on. It only needs 4 people to disagree. And I find myself being hit with this whenever I praise a Chinese company, for example. I mean people will upvote if I praise Microsoft, but certain Chinese companies or perhaps Russian ones will get me hit with downvotes to -4.
I do believe trolls should be censored. If anyone goes around asserting the world is flat, that's in bad faith and should be deleted.
What of the guy who brings up the idea that certain vaccines are not properly scienced with evidence? In HN, that gets downvoted to a -2 or so. But systems can be corrupt. I've done corrupt research but frankly nobody would listen to a high schooler's word against professors. I tend to be sympathetic to these, even though very often, it's just more trolls. These are still visible, but out of the way. Bringing a discussion to the bottom of the page brings attention to it, so it's the opposite of censorship IMO.
Now the big thing is anti-corruption agencies. Because ironically, they're a nest of corrupt individuals. You know in a movie that the Ministry of Truth is always the corrupt one, lol. The ones in my country are a mixed bag - they catch the corrupt, but sometimes they kill the people who report corruption too. They're effectively inquisitors; they step above the lines of justice by having a high error rate but they catch the criminals who use red tape as a shield.
If you were corrupt, you would 100% want to censor anti-corruption agencies, and this is the line where censorship should be held back.
What people generally censor on HN is the idea that wages could be lower, that jobs could be outsourced, that tech which reduces employment is profitable. Or that their cushy job causes environmental and ontological damage. This kind of information should be challenged too, otherwise you end up with people insisting that you should be paid a bazillion dollars for level 63 like they do on Blind and Instagram. Lack of censorship also leads to false information.