Violent attacks on U.S. diplomatic outposts across North Africa and the Middle East have once again raised the question of how to respond when Americans and other Westerners engage in provocative expression that others consider blasphemous. Though the attack on the U.S. diplomatic mission in Benghazi, in which Ambassador J. Christopher Stevens and three members of his staff were murdered, may well have been planned, as the State Department has maintained, the killers clearly exploited the opportunity created by outrage at an anti-Muslim film produced in the United States.

There have been several episodes in recent years in which perceptions of blasphemy have led to threats of violence or killings, starting with the publication of Salman Rushdie's novel "The Satanic Verses" in 1988, and including Danish newspaper Jyllands-Posten's cartoons of Muhammad. In the Netherlands, Theo Van Gogh was murdered in Amsterdam in retaliation for his film "Submission," which criticized Islam's treatment of women.

Even some who defended freedom of expression in those cases may be disinclined to do so now. This time, the film that triggered riots in Cairo, Benghazi, Sana, and elsewhere is so crude and inflammatory as to seem clearly intended to elicit the outrage that it produced.