And I am not proposing a mere correlation between extremist Islam and suicidal terrorism. I am claiming that the relationship is causal. There are many ways to see this, and not too many ways to credibly deny it (though Robert Pape keeps at it by skewing his data with the Tamil Tigers).
The first sign of a religious cause comes from what the terrorists say of themselves: al Qaeda and its sympathizers have not been shy about discussing their motives in public. The second indication is what they say when they think no one is listening. As you know, we now have a trove of private communications among jihadists. The fine points of theology are never far from their thoughts and regularly constrain their actions. The 19 hijackers were under surveillance by German police for months before September 11, 2001 (read Perfect Soldiers). Islam was all that these men appeared to care about.
And we should recall how other people behave when subjected to military occupation or political abuse. Where are the Tibetan Buddhist suicide bombers? They have the suicide part down, because they are now practicing a campaign of self-immolation—which, being the incendiary equivalent of a hunger strike, is about as far from suicide bombing as can be conceived. And where is that long list of Palestinian Christian suicide bombers you’ve been keeping in your desk? Now would be a good time to produce it. As you know, Palestinian Christians suffer the same Israeli occupation. How many have blown themselves up on a bus in Tel Aviv? One? Two? Where, for that matter, are the Pakistani, Iraqi, or Egyptian suicide bombers killing for the glory of Christ? These Christian communities are regularly attacked by suicidal jihadists—why don’t they respond with the same sort of violence? This is practically a science experiment: We’ve got the same people, speaking the same language, living in the same places, eating the same food—and one group forms a death cult of aspiring martyrs and the other does not.
I'm still going through the exchange. It's been a fascinating read thus far, and I encourage you to read the whole thing.