The previous system failed catastrophically. But the attacks didn’t succeed because it was a private system. The attacks succeeded because — quite simply — we lived in a pre-9/11 world, one in which knives and box cutters could be carried aboard U.S. airplanes.
The attacks succeeded because of the policy that required cooperation with hijackers. Not because knives and box cutters were allowed.
There is absolutely no reason to screen passengers for knives, box cutters or even guns any more because that policy is no longer in effect. After 9/11 it is no longer possible for anyone to hijack an airplane. The pilots won’t open the cockpit door, and as has been shown several times, the passengers will fight back against even suspected terrorists.
I’m sure someone could still blow up an airplane because explosives screening in US airports is completely ineffective. The only reason it hasn’t happened yet is because no one has seriously tried. Underwear bomber? Shoe Bomber? Give me a break. Those were not attempts to blow up a plane. Those were social engineering actions by the terrorists designed to cause confusion and create fear among the flying passengers.
The terrorists are working inside the TSA’s OODA loop and unless the TSA stops trying to prevent 9/11 from a 9/10 mindset it’s only going to get worse.