Companies who run social media sites are not in a position to be journalists, or even editors. They are mostly moderators, trying to navigate around regulatory rocks and PR disaster storms. I suppose they would happily not curb any speech, just because it increases engagement (and with it, ad revenues).

Actual journalists, that is, people reporting things, are those who have to demonstrate the ethos. But in social media, the people who white the posts are the users, in other words, ourselves.