The real cause of 9/11 was LACK of security period. It would not have happened at all if the airlines weren't so cheap in paying for proper and rigourous security procedures and scanning equipment, if airports enforced this policy and if governments took the initiative to pass laws BEFORE all this happened (for once - something today's PATHETIC little leaders don't know anything about - the only thing they seem to know is how to get votes).
So the security we see today, while sometimes emphasizing the wrong thing and annoying travelers for the wrong reasons, is a result of this reaction to its complete lack thereof before 9/11! Look at airlines like EL AL - their security was second to none (due to regional circumstances leaving them no choice) - and other airlines could have followed in their tracks long BEFORE 2001/9/11 happened for the terrorism threats to airlines began 30 years ago - in the 1970's!
Of course, this doesn't mean that security measures today should not be modified and fine-tuned.
John