The easy answer is it's a Muslim / Christian thing but I don't think that's the case. You listen to the average, man-on-the-street type person and they have admiration and respect for Americans and Western life styles. I think it's a political control issue where the middle east religious fanatics who are using religion to control the population and politics to their advantage and see the West as potential influencers who will disrupt their power and position with the talk of democracy.
The simple answer is religion or rather the belief that one religion is a better religion over another. But keeping it simple it is all about religion; that and OIL. I challenge you to read both the Koran and the Bible and come to a different observation.