Security theater didn’t do it.
Reinforced pilot cockpit doors and locks DID.
I’ve often wondered if the 4 pilots of the 4 airliners involved in 911 had had the ability to flip a switch or push a button and the ventilating system of the plane immediately dispensed a gas that put everyone outside the cockpit to sleep in a matter of seconds including the hijackers.
The pilot then lands the plane and opens the door for the cops. Or, better yet, he gets down to 10,000 feet, opens the door and throws the hijackers out the door (legally).
“Reinforced pilot cockpit doors and locks DID”
Absolutely correct.