There's even more to it, but let us just look at it this way ...

If you had a house with several entrances and only locked one of those entrances, would adding another lock to that one door increase your security? Would adding two locks to that door increase your secuirty? Would putting an armed guard at that one door increase your security? Would strip searching everyone who came in through that one door increase your security? No.

Assuming passengers represent a danger to air transport, the showy checkpoints are a futile attempt to make up for the inherently flawed "sterile area" concept.

The TSA is a political solution, not a security solution.