Voat and Gab seem to have done. Which ones haven't?
The way it seems to work is that unmoderated forums attract the toxic bigots that aren't allowed to speak their minds elsewhere, and they attack anyone who disagrees with them until most of those people get tired of it and go elsewhere, leaving the forum to the jerks. (Or else the owners have second thoughts and start moderating.)
It happens to any unmoderated forum that gets large and popular enough.
But bigots are allowed to speak their minds elsewhere, in many many places, especially in private, hidden from people who don't like them. They don't naturally gravitate to any place that lets them spread their ideas.
What I've seen happens is different, no actual genuine bigotry, but some organized effort to spread hateful propaganda and moderators not banning any of that, taking sides, especially when the organized effort comes from the government and is supported by mainstream government propaganda, so the moderators are naturally conflicted. Owners, moderators sometimes realize it's hurting the site, but still don't like to compromise on their views and eventually ban entire topics, not hate, personal attacks or anything like that and still being soft to the views they share even if they are against new rules.
> They don't naturally gravitate to any place that lets them spread their ideas.
Why wouldn't they? Everyone else does, you and me included.
Voat was a tiny site of 30,000 users in April 2015. Two months later, Reddit banned r/ShitN*ggersSay, and Voat's user base exploded. That was four years ago. Go take a look at the front page of https://voat.co/ right now. Don't do it at work, though.
The way it seems to work is that unmoderated forums attract the toxic bigots that aren't allowed to speak their minds elsewhere, and they attack anyone who disagrees with them until most of those people get tired of it and go elsewhere, leaving the forum to the jerks. (Or else the owners have second thoughts and start moderating.)
It happens to any unmoderated forum that gets large and popular enough.