Well, 9/11 happened because the government had for years told airline staff and passengers to simply remain passive, keep their mouths shut, and obey terrorists' commands during hijackings, since Uncle Sam would free them once they reached Cuba or Libya. This goes back to the Palestinian/Red Army Faction hijackings of the 1970s, altered slightly by the airline bombings of the 1980s, which brought us airport metal detectors. As a result, Al Qaeda led the sheep to slaughter on three of the four airplanes during the 9/11 attacks (The passengers of United 93 of course fought back after they learned what was going on from family cell phone calls).
Being a frequent business flyer myself (not by choice), I can safely say that another 9/11 is a virtual impossibility, not because of DHS or TSA, but because of better informed passengers, who will most certainly stand up together should a terrorist suddenly jump up in mid-flight and shout "Allah Ahkbar!"
You and I are on the same page. All the government needed to do after 9/11 was beef up the pilot area as they have and issue the following statement:
“You know that plane that lawn darted into a field instead of hitting it’s target? Well, if someone tries to hijack your plane, do what the passengers on that plane did.”
Two things would result. First, the hijackers would probably never get to a point where the plane would crash because of the ensuing fight and, second, hijackers would be on alert that unless they had a fully auto “assault rifle”, the only thing they would accomplish is their own death and that of a few passengers, so it is unlikely it would ever happen again.