@avlcharlie Do you believe that about only social media, or do you believe it about everyone?

Should Walmart be responsible for defamation in a movie just because they choose to sell some movies but not others?

Should a grocery story be responsible for libel posted to its public tack board without its knowledge, just because it clears out old posts from time to time?

Does a coffehouse become responsible for the speech of all patrons in its establishment because they put up a sign that says "no politics"?

Should you be legally liable for every post you boost just because you don't boost every post?

We all have a free speech right to curate our own spaces and choose who we want to allow in. If you were to impose the restrictions you describe, then you'd be trampling on those companies' free speech right to disassociate from you.