So if 1% of the population are far-right extremists, but most normal platforms ban or restrict them, any new platform with poor regulation will tend to fill with them.

I do think that the very extreme (and thus bannable) far right _are_ probably more common than ditto on the far left; you just don't get that many Stalinists, anywhere. But the normal left (and normal right) aren't generally nasty enough to get banned everywhere, so most of the internet's displaced population of commenters is far right.

I think there is an aspect of option 1, too, though. In Ireland a while back we had a referendum on allowing same-sex marriage, which passed by 62%, and another one, on legalising abortion (until then only legal in very limited circumstances), a few years later, which passed by 66%. Now, if you'd gone based on web polls and opinions being expressed in the comments on mainstream sites, you'd have assumed that both would fail by a landslide; it was really kind of incredible. Comments on news sites etc were grossly unrepresentative of the actual public mood; the right really does seem to be a lot noisier.