The constitution guarantees free speech, but not free drug use (though maybe it should). So I don't see any contradiction here. Meta has every right to police speech as it is a private company, but it has no obligation to do so.
Note incidentally that "free speech" doesn't mean you can say what you like. Yes, you can go out in public and swear and engage in hate speech - all legal - but for example you can't incite others to commit crimes, cross over into disorderly conduct, shout "fire" in a theater, etc.