Simply put, that goal is impossible to achieve. Any terrorist organization, given enough time, money, and people, can do damage to any particular flight or airport. Even I, with very little training, can come up with unbeatable scenarios.

It's the same way with my car. Yes, I've got a security system on it. That won't stop someone from stealing it if they're determined enough. Heck, all they've got to do is get a tow truck and they can steal the whole thing. But since most thieves don't have tow trucks, all I'm trying to do is discourage the guy who wants to break into my car enough so that he decides that the risk of detection isn't worth the effort.

That's what airline security should be trying to achieve. Absolute security is a myth. The question really should be: what levels of security are possible, at what cost (both in terms of restriction of liberties as well as money spent)? And then we can have a rational discussion as to whether the benefits of a given level of security justify the cost --- and reasonable people can hold different positions on those questions.