DD:
Well, you caused me to read up more on the case histories here and it's maybe a closer case than I'd thought.... The phrase originated in opinions from the supreme court (Schenck v. United States, circa 1919) was where Holmes used the example of someone falsely shoulding "Fire!" in a crowded theater... But this case interestingly is about a guy who was encouraging people to resist the draft, which Holmes concludes is was NOT protected speech. Why does Holmes conclude this? He writes:
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.
In the late 1960's Brandenburg v. Ohio comes in front of the court (a case about the KKK). Brandenburg is on trial for hate-speech, on the grounds that it could incite violence, and as a result be restricted by the "clear and present danger" clause.
In this case, however, the court finds for Brandenburg, and establishes a new standard (unfortunately named for the case, and in this case, the KKK nutball himself). The standard is (and remains now) the "imminent lawless action" test, in three parts. Effectively the speaker must INTEND the violence as a result of his action (e.g. not be a comic telling a joke, which is protected), the violence must be IMMINENT (today, not next year), and the violence must be LIKELY.
It's hard to argue that our Koran Burner doesn't meet the test. He can claim he doesn't INTEND it, I guess. Also unclear if violence incited outside the USA should be considered in this case.
But, in summary -- burning the Koran appears much closer to UNPROTECTED speech/expression than I had thought. I still think it's ridiculous that the crazy guys in the room get to effectively set the standard for this--which I suspect would be the dicsussion point should this issue ever make its way to the courts.