"I'm all for freedom of speech - but you don't have the right to shout fire in a crowded theatre."
This vulgar paraphrase of the hackneyed dictum of Judge Oliver Wendell Holmes Jr, so beloved of cliché-mongers, is interesting only in that it leaves out the most important word in the noble judge's sentence, which actually reads: "The most stringent protection of free speech would not protect a man falsely shouting fire in a theatre and causing a panic." That word is "falsely". What Wendell Holmes meant was that you don't have the right to shout fire in a crowded theatre when you know that there is no fire. This, the First Amendment would not protect.
The "falsely" bit matters, because if you do notice a fire, you surely have the right to alert people to it fairly volubly. Some people might get hurt in the ensuing stampede, but not as many people as could get scorched in the inferno.
As we are now reminded on an almost daily basis, Britain has no First Amendment. So when David Miliband used Wendell Holmes to justify the ban on Dutch MP Geert Wilders from entering the UK, it hurt for more than aesthetic reasons. "We have profound commitment to freedom of speech," said the British Foreign Secretary. Anybody hear the "but" coming?
"But there is no freedom to cry fire in a crowded theatre."