When yelling fire without a compelling reason, a reasonable person would anticipate everyone else's standard reaction, and that in the course of that action injury and/or death might occur.
Which is why culpability in the US depends on the speaker's intent. What if I believed I smelled smoke and yelled "Fire" because of that? But was simply wrong?
Unfortunately, intent is impossible to prove definitively, without actually peering into someone else's mind. Thus, can of worms.
"Shouting fire in a crowded theater" is an analogy that was used to justify banning antidraft activism in the first world war. It is very much allowed under current precedent.
"Directed to and likely to incite imminent lawless action" is the current standard.
https://en.wikipedia.org/wiki/Shouting_fire_in_a_crowded_the...
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)