Many people, both anarchists and non-anarchists, would strongly disagree with that statement. And not all of those people are uneducated edgelords whose main argument is that it's a slippery slope.
I find it ironic that the same people who question whether or not Facebook should be allowed to do this seemingly have no problem with the moderation on Hacker News. Trump’s account would have been restricted within days here after repeated warnings. And yet few seem to question that @dang’s moderation is precisely how we continue to (mostly) have high-level, thoughtful discussion around these topics. Fewer still question HN’s right to perform moderation in general.
And yet when it comes to Donald Trump’s calls—from a seat of power—to overthrow the results of free, fair, and democratic elections so that he can stay in office, we’re supposed to simply throw our hands up in the air and accept it? When he uses thinly-veiled (and sometimes completely open) language encouraging his supporters to use violence to achieve his goals, we’re supposed to accept that there’s just nothing to be done?
Anyone making this argument should be deeply, deeply ashamed.