Then why is it a crime to cry "fire" in a crowded theater?
It's not against the law:
[[It's Time to Stop Using the 'Fire in a Crowded Theater' Quote
Ninety-three years ago, Justice Oliver Wendell Holmes wrote what is perhaps the most well-known -- yet misquoted and misused -- phrase in Supreme Court history: "The most stringent protection of free speech would not protect a man in falsely shouting fire in a theatre and causing a panic."
Without fail, whenever a free speech controversy hits, someone will cite this phrase as proof of limits on the First Amendment. And whatever that controversy may be, "the law"--as some have curiously called it--can be interpreted to suggest that we should err on the side of censorship. Holmes' quote has become a crutch for every censor in America, yet the quote is wildly misunderstood.
But those who quote Holmes might want to actually read the case where the phrase originated before using it as their main defense. If they did, they'd realize it was never binding law, and the underlying case, U.S. v. Schenck, is not only one of the most odious free speech decisions in the Court's history, but was overturned over 40 years ago.]]
http://www.theatlantic.com/national/archive/2012/11/its-time-to-stop-using-the-fire-in-a-crowded-theater-quote/264449/