The best subreddits (askhistorians, etc.) will instantly delete low quality posts.
Reddit as a whole banning bad subreddits (fatpeoplehate, coontown) made reddit a better place for everyone, and the trash moved to voat which is barely active now.
Most big sites will now ban you for for threatening or very hateful speech.
Free speech is not the issue. No one is taking away free speech by banning you on Twitter.
Your free speech is taken away when something you say lands you in prison. Getting banned from a shitty private website doesn't violate your free speech rights in any way, full stop.
It is far superior to have bad ideas met with good ideas, than to have bad ideas circulate unopposed within unpopular groups.