The door itself is the cause of the problem - because it introduces a single point of failure in the pointy end of the plane.
Agree entirely. It was a stop-gap measure taken in haste to respond to a specific method of attack. Most sane people knew on 9/12/01 (or uh 12/9/01, if you prefer), that no one was going to be able to commandeer a jet with some sheet metal razor blades again. But our security measures are ever reactive, rather than proactive.