They were able to take over four aircraft because airline policy at the time forbid any resistance to a hijacking attempt. What the 9/11 hijackers used - knives, box cutters - is irrelevant. They could have been successful using a ball point pen - not a prohibited item, by the way - held to the throat of a flight attendant.

Airport security has been stepped up since 9/11 - in the guise of TSA's Kabuki theater - because government felt it had to "do something" for public consumption. I know this to be true, because I attended many of the interagency meetings that eventually spawned TSA and DHS.

Late in the Bush Administration, at the direction of the Homeland Security Advisor, an interagency group of aviation security experts spent over a year analyzing the risks to aviation security. Thei report was rejected by Kip Hawley and Mike Chertoff because the real experts had the audacity to reach a conclusion that undermined the TSA Security Theater. Their conclusion? That "under the wing" security was a far greater threat to aviation security than the threat posed by passengers.