Small, niche communities, and unfortunately you'll probably need to know what ideas you're interested in ahead of time to get there.
People with intelligent but divergent ideas are always outnumbered by people pushing an agenda, and they end up getting moderated together because it's hard to superficially know the difference.
Note that it's entirely possible to have an echo chamber that's divergent from bigger echo chambers, and that's were a lot of people are pointing you, because of the instance you asked on.