I know you are all waiting for the Voice of Reason, so here I am.
1. This is not a First Amendment issue. No private entity is obligated to provide a platform for free speech.
2. It was probably unwise (though perfectly legal) of Discovery to boot the guy, but this remains to be seen. My prediction: they will let him back on the show.
3. You don't want to know what my opinion of his opinion is.

(Though, of course, you probably do know.

) And, of course, AFF is not obligated to provide a platform for my opinion.