You are making some wild and crazy assumptions there. Suppose there is a test - something as simple as a metal detector - that flagged 10% of the people. If the light on this test turns red, the person deviates from the main line of people and walks through a second detector that costs a little more to run. Also, being a second detector, it would create a second bottleneck if everyone had to walk through it. This second detector only flags 10% of the 10% that go through it. So, the "more expensive" and "more intrusive" test isn't what you are assuming it to be. It is not a complete strip search. If the second test flags a person, then the person goes to a more precise test. This continues by only expending security where it is needed.
It is also a wild and crazy assumption that walking through a detector 10 times will cause it to pop positive at least once. I have never ever caused a metal detector to go off. I fly very often. I work in a secure building. I do a lot of government contract work in other government buildings. So, I figure that I walk through metal detectors at least 20 times a week. A friend of mine had them go off on him a lot. They would baton him and let him go. He finally checked into it and found that his tie clip would set it off if it was oriented just right. So, he tossed out the tie clip and hasn't set one off since. If you trigger the terrorist test, you should ask why. Once you know why, you can decide if it is worth changing. It could be something as simple as replacing a tie clip.
