> What if it turns out that white supremacists primary wish is to have their arguments heard by society, but society has instead cast them out and refuses to let them post elsewhere so they can only post on 8chan, and that some of them, mentally unstable, react to being outcast in extreme ways?

The thing is, their argument is often not coherent or unfunded and once public, will be shown wrong pretty quickly (sadly not always with the right words or the right ways) and they'll feel attacked because of that.

On theses platforms, that doesn't happen, people are cheering them, they feel right, they feel it's the correct way of thinking. Thus they go there instead because it feel good.

The best example is r/the_donald banning any opposite way of thinking.

They are also slowly self-justifying isolating themselve from others, accusing others of manipulations, of fake news, using conspiration theories to ignore facts, accusing people of "concern trolling", etc...

That's sadly quite hard to fix and you'll need quite a b it of motivation and original thinking to be able to go beyond all theses walls they build arround themselves to protect their hatred and their little communities.