I've just come back from a late screening of United 93. Paul Greengrass is a good craftsman (or he was with Bloody Sunday). If I ever go to Shanksville, Pennsylvania I will put a flower on any memorial to the passengers and heroes on that plane.
But this film will do little more than add to US national stupidity. With no context, and no requirement to learn about the context within which these atrocities arose and why, the film will lends itself to stirring up more brute force and bloody ignorance, and greater catastrophes in future.