Not to be pedantic, but what does "quantifiability" have to do with the subject? Obviously, TSOs cannot measure their courtesy "level" with a machine, not can they measure the subjective dispositions of those transiting the checkpoint scientifically. Civilized human beings (TSO or pax) regulate their interactions with others partly by intuition of the others' dispositions, and partly by a desire to err too much on the side of courtesy. Whether there is any true charity in this desire is beside the point -- it helps to grease the wheels of social interaction. For those who try to keep even a minimally higher standard, the age-old and almost universal adage commonly known as "the golden rule" applies. None of this is quantifiable; all of this is partly subjective but partly based on the quasi-universal expectations of civilized people.

One hallmark of civilized human behavior is frequent self-examination. This is not compatible with dismissing the importance of courtesy due to the "unquantifiable, subjective" nature of that "fine line."

I have argued before in this forum that the keys to "fixing" the TSA (if that be possible) are common sense and courtesy. As another poster has said in this thread, legal hair-splitting (though it may have a certain place) is beside the point. The human element is precisely what is being overlooked by the authorities. Anyone who can glibly answer that such subjective factors do not translate well into the minutiae of SOP may be doomed to a lifetime of perplexity at the (understandably) negative attitudes of the traveling public toward the TSA.