Forgetting the koran, (because that one will never be resolved), Imagine you were in Kefah shoes, you were living your life (although not perfect), in relative safety, now he being controlled by an occupying force, and there is death all around, it would seem he is getting from all sides. What would do, to rid the US of those who kill those around you.
Plus remember that a US soldier (along with many of the allies) are there by choice, they are not conscript soldiers.
Kefah has always separated combatants from non combatants.
I am not defending the killing of allied forces.