Earlier quoted context omitted.
They aren't in violation of current anti-trust laws (AFAIK), but if the problem is that companies have grown so powerful that they can control speech, that has parallels to the problem of companies growing so powerful they can control prices. So what I'm suggesting is, why not create new laws that target the biggest platforms, using the same framework as existing anti-trust laws?
Can you explain how twitter is controlling the speech of a newspaper by blocking its article on their platform? Does twitter blocking the article suddenly unpublish it? Should conventional printing press owners be considered utilities because you might want to post a bunch of posters somewhere, and by refusing to print your posters they censor you?
The difference in the printing press analogy is that if a printing company won't print my poster, I can take it elsewhere.