Monday night's arrest of Faisal Shahzad, a 30-year-old Pakistani-American accused of planting a car bomb in Times Square on Saturday, will undoubtedly stoke the usual debate about how best to keep America safe in the age of Islamic terrorism. But this should not deflect us from another, equally pressing, question. Why do Pakistan and the Pakistani diaspora churn out such a high proportion of the world's terrorists?

Indonesia has more Muslims than Pakistan. Turkey is geographically closer to the troubles of the Middle East....