The higher criticism of Ms. Geller is that, while her constitutional rights are not in question, her judgment and wisdom are. I happen to think that Ms. Geller’s substantive contribution to the great foreign-policy debates of our time is roughly equivalent to Pat Benatar’s contribution to the Western musical canon, but that’s beside the point. Every healthy society needs gadflies, who contribute more with their sting than with their buzz. Ms. Geller is one of those gadflies.

In particular, Ms. Geller is hammering home the point, whether wittingly or not, that the free speech most worth defending is the speech we agree with least. That’s especially important when the enemies of free speech—in this case, Muslim fanatics—are invoking the pretext of moral injury to inflict bodily harm. A society that rejects the notion of a heckler’s veto cannot accept the idea of a murderer’s veto simply because the murderer is prepared to go to greater extremes to silence his opponents.

All the more so since the Islamist objection to depictions of the prophet—I say Islamist because there is a rich history of Muslim depictions of Muhammad—is far from the only Islamist objection to Western ways. Sayyid Qutb, spiritual godfather of the jihadists who attacked Ms. Geller’s event, spent the better part of 1949 in Greeley, Colo., and was scandalized by football, jazz and American womanhood, among other perversities. Should the polite consensus of American opinion concede the legitimacy of the complaint about cartoons, another complaint will follow.