I don't think it's quite as simple as "X" did it or "Y" did it. Rather, I believe it's a combination of all the suggested causes, to varying degrees. The question is to what degree each factor is responsible, and at the present time that's open to interpretation and opinion IMO. Perhaps history will tell, but that's for the future to decide. I accept that "kill the infidels" is one of the factors, but in my opinion the "blowback" factor is greater, and the "envy" factor is lesser.