This looks like an expensive lesson, or maybe a slightly cheaper one if every lawyer he asks to take the case laughs him out of the room. May he learn what his actual rights are and are not.

"Freedom of speech" only applies between people and the government. In a private setting, all bets are off. Any attorney who takes the case is a shyster, willing to take your son's certain loss to milk him with fees.

Freedom of speech applies to the government not restricting your speech, and there are exceptions. Your son needs to learn that yes, we have freedom of speech, but we are not free from the consequences of that speech. And no attorney is going to touch this. Unless they just want money even though they know it's a losing case.