HN has plenty of rules that remove content "based on the content itself". For example, HN bans job ads (outside of 'who is hiring' threads). There are no circumstances where a job ad post is allowed outside of 'who is hiring' and YC-funded companies, not even "in good spirit". Similarly, the HN FAQ says not to post comments complaining about paywalls, and there is no 'unless you are civil' exception.

Again, does banning content from an internet forum inevitably lead to "oppression" or "bad outcomes"? If so, why hasn't this happened to HN/Reddit/Twitter/etc?

As someone who did a lot of moderation in the past, people forget any platform is more akin to a cafe, instead of a public square. A cafe has rules that keep a pleasant atmosphere. A public square has a public function and needs rules to allow for a broad discourse or protests. One could argue if there is a certain size where a platform like youtube becomes a public square. But on the whole its their room, their rules.

I disagree. Aggression in the sense of language style, is very much in the eye of the beholder. As is assigning value to a ‘flamewar’. One person’s meaningless flamewar is another person’s valuable but heated argument.

Not any more so than physically.

Sure, if you stop something early you may have overstepped, but no one questions violence taking place when rocks are being thrown. Same goes for once a discussion degrades to ad hominem attacks/insults.

This is simply not correct.

You may call something an insult or an ad hominem as a third party, but you cannot know what value the consenting parties are gaining from the fight.

If you claim that you do, you are asserting that you know better about their experience than they do.

I’m not saying there is no room for third parties to intervene, but I question the judgement of anyone who thinks it’s that easy.

There are good reasons why people choose to engage in combative dialog, although it may not be obvious to observers.