A couple of points I think people miss (and have done so since 9/11)...
How do you tell if a security measure is working? Well, what you're securing against doesn't happen. Can you be 100% sure that it's the security measure, or some other variable? No, you can't.
Locks keep honest people honest. Security checks often do the same. But, if you're a terrorist, and you have the option of going route A, which has 10 checks, and route B, which has two...you'll pick route B.
I travel a lot, and I travel with some CRAZY stuff. Multifuel tanks for camping stoves, a set of Wustoff cooks knives, dive computers (I'll explain why that's crazy). I also get to the airport early, explain to the check-in person what I have in my bag, and request a search if I think there's going to be a problem. Takes a little longer, but not as long as a funeral for 400 people.
The "crazy" dive computer. My wife dives with an Aeris Atmos 2 with a quick-disconnect. The computer weighs about a pound. Has a little LED clock that comes on with a push of a button, right over the SPG, which won't move unless hooked to an air source. All sealed in a watertight, gas-tight rubber case.
Think about that, and think about how much explosives it takes to blow a hole in an airplane hull.
About a pound.
So you have your explosive (which, to the well-seasoned European traveler, would be easy to come by), a detonator (a blasting cap made from gun powder or scraped match heads), and a timer (the computer itself...doesn't even need to be modified). All wrapped up in a casing that a human won't be able to smell through. A dog might be able to.
So, even the "obviously safe" items can be modified. Great...I should be in the FBI's office soon.
Finally...profiling Arabs, because there's no way a 22-year-old white American college student could ever be...well, except John Walker Lindh...but other than that...well, Patty Hearst...but aside from those...nevermind. When you try to defend everywhere, you defend nowhere. And a security check is only effective when it is random, because a 100% check establishes a pattern that one need only study to circumvent. Think about what you pack, notify, and if you're picked for a search (if you don't volunteer first), deal with it.