Airport security is a joke.
No matter what you do, it will be possible for someone to hijack a plane. There is no way to stop a truely determined terrorist from killing people. None.
We live in a free country, and the price of freedom is our security. Freedom is not cheap, and the cost is people dying. We can work to prevent it, increase security to a point. But when it comes down to it, there is little we can do to stop anyone truely determined to attack us, short of becoming a police state.
There is nothing more important than freedom.