You can say whatever you want.
But when you take an illegal action (or, grey area, compel someone else to take an action) then you lose free speech protections.
"Fire" in a movie theater is the classic example of the court deciding what sort of speech consitutes compelling action.
This in contrast to other many other countries, where there is no guarantee that speech-that-does-not-compel-action will always be free.
To me, speech vs action is a critical distinction, because it prevents anyone in power from monopolizing the marketplace of ideas by banning an idea itself. While simultaneously preventing the worst societal consequences from actions.
Or, in other words... neo Nazis should be allowed to march peacefully... but so should everyone else. And the latter should massively outweigh the former. (That said, nothing prevents keeping a much closer eye on violence-espousing neo Nazis)