You choose to type h t t p facebook dot com into your browser.
They have absolutely not power in what you see or read, you go there voluntarily. Just stop going there.
True, but that's for people who are awake; in this case, we're not actually dealing with (sane, rational, critically thinking) individuals, but with statistics. Nobody cares about individuals denying the holocaust or whatever, but when it becomes a movement, or a feeling, or a suspicion in enough people, it becomes a statistically significant trend that can influence politics, elections, votes, etc.
I mean there's tons of anti-intellectualism going on now wrt anti-vaxxers, flat-earthers, corona-deniers, obama-is-a-kenyan-lizard-man, trump-is-immune-to-the-rona, etc. These are rational individuals, they may not be on Facebook or they may, it doesn't really matter because in the end it's a numbers game.