So if a citizen comes to the security station with plans to crash the plane, you consider that treating the person as a "citizen" is the priority job. See, the trouble is that people have this unspoken prejudice that terror is something done to "citizens" by "foreigners". I think the dead babies in Oklahoma City would wish that were true.
No basically, citizens vs. noncitizens is not the dichotomy. Peaceable travelers versus conspirators is the one that counts. But I don't think that requires TSOs to abuse people not protected by the Constitution. If you are the peaceable part of the dichotomy, their job is to insure your peace remains intact. I don't think the Constitution is their primary concern. That concern has been addressed in Congress and the court system. Anything that these two bodies says is legal is, under our system of laws, legal. People who don't like that should emigrate to a desert island.