You neglected to mention that since 9/11, it would be almost impossible to do now what the hijackers did then. If that were attempted now, a whole plane load of vigilantes would rise up against the hijackers.
It's a pretty simplistic viewpoint to think that nothing should have been done to amp of security and the problem would just take care of itself after the tragedy of 9/11. Yes, maybe the exact same plan wouldn't work again, but downing a plane would take far less compliance by the other passengers than running it into a building.
Sure, sure... And you know this how? A gut feeling? Remember, there were multiple planes on 9/11, and this did not succeed or happen in any of those situations.
I like that you are so sure about this, with no data or anything.