1. The passengers and crew of a plane bear the ultimate responsibility for the safety of an aircraft. When you are in a sealed container miles above the ground, and somebody is trying to blow up the plane or stab the pilot to death, don't sit around and wait for help to arrive.
2. You have to give the current system at least partial credit for saving the lives of the people on the plane. The use of metal detectors at airports means that would be bombers are prevented from using bombs with metallic content. That means that they can't use switches, wires, shrapnel, or blasting caps. Which in turn means they are forced to awkwardly light a fuse while surround by nosy passengers.
3. Al Qaeda appears to be playing a game in which each attack means that passengers must endure more indignity. After 9/11, you had to throw out your nail clippers. After the Shoe Bomber, you had to start taking off your shoes. Now they are talking about using body scanners. How long before passengers are required to undergo a colonoscopy?
4. I propose an experiment. Let's have a experimental group of flights in which security procedures are changed with every new attack, and a control group of flights in which procedures stay the same. My hypothesis is that the control group will be more popular for passengers, and that the experimental group would have more terrorist incidents. Terrorists like it when their $50 bomb causes us to spend $10 million more on equipment. Also, I'm guessing that squeamish people make more attractive targets.
5. It's important to keep the hazard in perspective. The reason why terrorists attack airplanes is because it gets more headlines than other forms of carnage. People will remember a failed airplane bombing longer than a successful mass shooting.