> I really don't see the mystery here. We have a group that is
> trying to achieve political goals by killing innocent people.
You're being obtuse. The mystery is what exact ends they're trying to bring about. (Like I said, it's probably pretty easy to come up with a comprehensive list of candidate motives, but at the current moment doing any more is impossible.) Some would say that the restoration of the Caliphate is a senseless end. I wouldn't disagree.
And of course, even worthwhile ends can be pursued via senseless means. Imagine the following dialogue:
A: The American occupation of Iraq is senseless. B: What are you talking about? We're trying to clear the grounds for freedom and democracy in the Middle East. A: Even if that's what "we" are trying to do, the current occupation isn't going to work.
-- Luke