And all the hijackers presumably had to show ID to board the planes.
Actually I believe they all did show ID's and succesfully boarded. And your point? Oh, I know. We should never under any circumstances show ID's because of our right to not show ID's as written in the constitution (I forget again where is the ID thing written there?)
(And now I'll wait for all the constitutional scholars here to respond about the various amendments protecting rights against search and seizure, etc.)