You named the only two relatively free, large, unmoderated public forums with transparent-able feeds. Well Reddit’s feed is transparent: Lower bound of Wilson score. On Twitter, I only filter for latest, but you cannot do that on Facebook.
Feeds suck, sure, but there's really no censorship for anything about communism etc short of calling for violence against wealthy people.
Facebook is less "free" in that regard since they won't allow "all men are trash", which Twitter would only go after if you qualify it with a race that is considered 'protected', and Reddit would probably ignore completely (but "local" mods might not, which makes Reddit take a special role there).
