I know during my recent trip to Japan, the differences between the TSA and their foreign equivilants were quite striking.
While in line at Narita Int'l, if something was expected of you, a person would walk up to you and ask you in a soft voice if you would do what was needed. Getting back to the US, they would just scream at the top of their lungs over and over (and over and over.......).
In Japan, if a new line was being formed, a worker would walk up and point out where they needed/wanted you to stand. US: yep, you got it. More screaming.
Now I know that part of it may be that it was LAX and it is a very busy airport so TSA member's patience is probably frazzled but I am relatively certain that Narita Int'l is every bit as busy yet everybody was much more relaxed and as a result, things went a whole lot smoother.
I do think that part of it is to an extent a power trip. They are essentially working without fear of any consequences because all they have to say is the magical words "I felt they were a security risk" and they are in the clear.
Sometimes the way things are done in the US just makes me shake my head.