I am surprised that pedantic-lawyer Tim does not also point out the origin of that phrase.

Specifically, the case Schenck v United States in which "falsely shouting fire in a crowded theater" was used as an analogy for protesting the draft.

I have therefore always been troubled by the origin of the phrase, even though it feels like a reasonable exception to make.

Edit: And now I see that Vladimir_M has already posted this.