To be sure, America is a more "religious" country than Germany. In the U.S., nearly 40 percent of all church members attend divine service every Sunday; in Germany, only about nine percent do so, and among Protestants the figure is even more lamentable - four percent.

Arguments about the merits of religions are often battled out with reference to history, by comparing the sins of theists and atheists. (I see your Crusades and raise you Stalin.) But a more promising approach is to look at empirical research that directly addresses the effects of religion on how people behave.

One woman who was attacked told her story with Pastor Lou Engle at the International House of Prayer in Kansas City. She said the group's fellowship had been peaceful for several nights before the riot.

"People would come stand with us and join us," she said. "We got to pray for some people."

But then angry men began yelling profanities and warning the Christians to leave the district.

(Warning: Video may contain offensive language)

On closer reading, Kalisch offers a far greater challenge to Islam than the secular critics who reject its claims. The headline that a Muslim academic has doubts over the existence of the Prophet Mohammed is less interesting than why he has such doubts. Kalisch does not want to harm Islam, but rather to expose what he believes to be its true nature. Islam, he argues, really is a Gnostic spiritual teaching masquerading as myth.