They are, though. Facebook moderate their content, sell advertising (and increasingly offer themselves as a marketplace for other goods and services) and offer you news items. It is a media company, the "social" bit is just a fig leaf to allow the company and those who shill for it (including very senior political figures) to pretend that what should be obvious to us all isn't actually happening.
As for US law allowing it, that really should not matter - US law also allows considerably more things to be said without being defamatory, but that isnt the case here.
they’re not publishers, that’s a simple fact has stated in law, no matter what your argument is. I don’t agree with it because it allows them to push any agenda they want with no repercussions. But is what it is.
would there be any difference if you owned a piece of land and dedicated it local artists to promote their artwork by graffiti (as done in the Baltic triangle a couple of years ago) and someone started right racist comments on the wall, are you as the landowner responsible for what others right or is it your duty to remove it and ensure it doesn’t happen again
like I said I don’t like the large social media companies, they have to much power for my liking