The biggest problem is getting the powers that be to admit that self-defense is a legitimate right. Control is the name of the game. Air marshals can control the passengers, pilots cannot. F-16's can control the situation that air marshals cannot. The government has the position of trying to contain terrorism and at the same time not trusting the public to do the right thing.
During WW II we had a good security system because we had the government and the public on the same side. We don't have a good security system now because of the government insistence that they must control everything.