Saying you have no moderation is attractive to one crowd in particular (there are other people who theoretically favour it, but practically they’ll use a moderated forum anyway). So you get a quick numbers boost but you’ve now fundamentally limited your audience to people prepared to share head-space with that crowd.
Reddit, Facebook and Twitter got in early and got to spend a lot of time learning on the job. Unless you start small, you’re not going to get that luxury now.
(Please don’t take this as an endorsement of any particular moderation policy, in theory or practice. Most of them are kind of awful at times. But the problem is hard.)
The only thing good are the vast majority of users here have good intention. If only HN had multiple boards with various mods.
But when you start to gain popularity, the way you treat "free speech" becomes an issue. Discord is not a great example in that niche communities are not scraped for web search (that I know of).
Twitch and Discord did well there for instance. Started out as gaming focused, then became more mainstream.
By doing this, you bring in non extremists early on, and tilt the audience pecentages in such a way that most regulars aren't such extremists.
The problem is most 'alternative' platforms market themselves as 'Reddit/Facebook/Twitter/YouTube except with free speech and no rules' rather than 'an art/gaming/music/sports themed alternative to Reddit/Facebook/Twitter/YouTube with free speech'.
Former means you draw in the outcasts and extremists, latter means you draw in another audience that can then be made more mainstream by opening up support for more and more fields of interest.