We don't NEED to improve security. The only thing we need to improve security was the knowledge that this was possible. This happened by the 4th plane, which didn't get to it's intended target because the passengers knew what they were up to, and didn't let it happen.

Everything else is merely an appearance of security. It has to be as visible and intrusive as possible to placate the PHRASECENSOREDPOSTERSHOULDKNOWBETTER..