>> There should be no reason for us to go through a body scanner if the TSA and DHS believe their background check and fingerprinting are effective.

The general concept of security in layers is perfectly reasonable because no measure can be 100% effective. Combining a few 99% effective measures can get you acceptably close. We do the same thing in cybersecurity.

That said, the TSA is still dumb because of how arbitrary and unfair the requirements can be.