John, you’re correct that Stone makes no attempt to explore the motives and psychology of the enemy. But he has made it clear that we Americans have an enemy and that he is a barbarian. He is evil. He loves death.
By contrast, we treasure life. Our enemy sees that as our weakness. We believe that in the long run it will prove to be our strength. We are, literally, betting our lives on it.
This is brought home by one remarkable character: a devoutly religious Marine (he hears God calling him) with no sense of humor. Stone does mock him as such warriors have been mocked in so much popular culture from M*A*S*H to “Apocalypse Now.”
At one point the Marine says that this attack will have to be “avenged.” That’s right: “avenged.” He doesn’t wonder why they hate us, he doesn’t fret about root causes, he doesn’t argue for a proportional response.
At the end of the film we learn that after 9/11, the Marine signed up to go to Iraq. Served two tours.