Given that say the Christchurch shooter live streamed on Facebook for 17 minutes but FB had no repercussions but Gab and 8chan did, you gotta really seriously think about who is dictating what you see on the web. Why does Facebook's wikipedia page not say they are a haven for mass shooters live streaming murders?
Facebook actually attempts to remove illegal and offensive content, though. Voat, Gab, 8chan, etc. pride themselves on deleting nothing. Nobody, Facebook included, can predict a live video of a shooting. You can't pre-emptively block a video. You can, however, see a pattern of content being posted and decide whether to ignore or act on it. This is what Reddit does when they ban subs like FPH, The_Donald, CoonTown, etc. They are actively taking steps to prevent such things. Your "free speech" sites don't do that, they let it roll and are consequently tolerant of such activities. I won't go so far as to say they advocate it (though I honestly think they do) but they actively defend its presence.
I was largely referring to American groups or companies that get horribly slandered on wikipedia and have no recourse. Take Gab for example, where the second sentence of the wiki article is literally "The site has been widely described as a "safe haven"[9] for extremists including neo-Nazis, white supremacists, and the alt-right.[10]"
Talk about slander about a website that just doesn't ban people for soeech.