All of the 9/11 terriorist could pass a criminal background check, and they all could go thru security checks done by airline pre-screening (computer background checks at the counter) So, with this in mind, why does the govt want another intrusion into your life?
because that way thewy can say "look, you see we ARE doing something about aviation security".
remember, although you can check the pilot for weapons as he/she goes through the gate, he/she can still hijack the aeroplane without one!