Do not have a business that relies on "growth & engagement".
The problems of large-scale social media are all due to them making money from "engagement" - it doesn't matter how disruptive someone is, they are "engaging" and producing content that others will "engage" with. Bonus points that harmful and divisive content tends to produce more engagement (from others being angry and arguing) than constructive content, so there's this perverse incentive where they have to pretend to forbid such content but often look the other way when it's posted up to a certain threshold (there's probably a formula that calculates the "optimal" exposure time for harmful/divisive content that maximizes engagement while not letting it stay too long for the media to get wind of it and cause a PR/regulatory issue).
Given the above, it's no surprise that any large-scale social media platform eventually devolves into a cesspit. The "moderation" they have is purely there to placate regulators but its actual quality is terrible, both in terms of false positives but also false negatives because investing into good moderation would be bad for business for 2 reasons: 1) it costs money and 2) it would catch a lot more harmful/divisive content that currently generates plenty of engagement. Being a cesspit is actually profitable as long as your competition is also a cesspit (which it will be as long as it has the same business model and incentives).
If your business model doesn't depend on engagement, then you can be much more selective and restrictive in the types of content you allow, and make rule breaking more costly (you can even charge for accounts which would make permanent bans cost more than just a new e-mail address). Encouraging quality over quantity also means there's overall less work for the human moderators.
Moderation is not some impossible problem despite what the large-scale social media platforms say. It's only impossible if you intentionally open the floodgates and encourage everyone to piss in the stream. But you don't have to open the floodgates. You can encourage quality over quantity and make it costly to break the rules. The reason HN works isn't because they have some secret sauce, it's just that they would rather have no content than bad content, while every social media website out there would rather have bad content than none at all.
