Behind California's Ban on Assault Weapons

[Kaleva]

30. Holmes used that analogy to support the " Espionage Act of 1917" used to squash anti-draft efforts

The Espionage Act of 1917, which was amended with the Sedition Act of 1918, made it illegal to distribute flyers opposing the use of the draft during WWI. This was challenged as being unconstitutional because it violated the right to free speech while the government's position was that such activities presented a clear and present danger to the government's efforts to recruit men for the war. The Supreme Court ruled in support of the legality of the Act and Justice Holmes used the analogy of falsely yelling fire in a movie theater in support of that decision.

"The most stringent protection of free speech would not protect a man falsely shouting fire in a theater and causing a panic. [...] The question in every case is whether the words used are used in such circumstances and are of such a nature as to create a clear and present danger that they will bring about the substantive evils that Congress has a right to prevent."

The 1969 Brandenburg v. Ohio case overturned that view and "limited banned speech to that which would be directed to and likely to incite imminent lawless action".

http://en.wikipedia.org/wiki/Shouting_fire_in_a_crowded_theater

The Brandenburg v. Ohio decision essentially prohibits the government from prohibiting anyone from falsely yelling "Fire" in a crowded movie theater. However, one still can be held liable after the fact for the consequences of their exercising their right to free speech.