Since you have read the Koran, as I have, then you should realize that there are reasons that explain their reasoning, even the crashing planes into buildings. It doesnt mean its right, but it is clear that it was not just an "i hate America" stunt, it was very well planned and they take it seriously. Nothing is above their God, and when someone threatens their beliefs as the United States did with Jerusalem, that was their reasoning. Im suprised that you have this notion of right and wrong when you say you have read and are familiar with these texts, i would think that would make you understand the term "belief" a little better but apparently not. You are right when you say there are things right and wrong, if you look at each religion there is, but if you look at everything as a whole, it is all "gray" because no belief or religion is better than another.
I just wanted to add im not coming up for a reason why the attacks on America should have happened, just trying to explain that things seem differently in the eyes of each religion.