They might just be full of alt-right because they are small and few. If there were more free-speech spaces they would fill with normal people, so you wouldn’t notice the alt-right, like you don’t in bigger platforrms today.
More free-speech plaforms could be a good thing. Like wikipedia and openstreetmaps - as long as the normal people drown out the crazies, it works brilliantly, much better than a more tightly controlled space.