Private companies can censure and ban all they want to. Free speech per the Constitution involves only government.
FB and Google and Twitter and others are utilities and need to be regulated as utilities. Amazon too.
Businesses can be sued civilly and (though rarely) prosecuted for criminally violating civil rights.
Corporations Have Paid Out at Least $2.7 Billion in Civil-Rights and Labor Lawsuits Since 2000
https://www.thenation.com/article/corporations-lawsuits-civil-rights/
Big Tech can be sued for systematically firing those who have religious and conservative political beliefs in their workplace AND systematically oppressing them on the platform.