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You can assume that security personnel are profiling your behavior at any moment in the airport, including by hidden cameras. The arbitrary search rules are designed to provoke you to see your reaction.
What if we ask this guy a question? What if we search his bag? What if we search his baby's bag? What if we single him out and put him in a room alone? What if we mock his smile? What if we accuse him of joking? Or of traveling with a stranger in line that he's never even met?
The next question following any of these questions is "How will he react. What will his face show. Will he gesture with his hands. Will he sweat. Will he raise his voice. Will he frown. Will he smile." Basically any response at may lead to an escalated response.
Folks, this isn't about finding contraband anymore. It's about prolonging encounters, and making those encounters unpleasant, to place the passenger (or crew member) in what amounts to a stress position. It's basically Gitmo-light.
The problem isn't really for people like you, who can sense the game, have read Kafka, and also know that somewhere in this system you have some rights. The problem is with the less sophisticated, including non-English speakers, or perhaps those with physical or mental ailments, who can only sense that they are being singled out. Freaking out, can, AND HAS, led to death by airport security.
And not only are they checking bags, they are taking information off laptops without warrant. See:
http://www.nytimes.com/2008/07/10/opinion/10thu3.html?_r=1&scp=1&sq=laptops&st=nyt&oref=slogin
Why would the do that, if all they wanted to do was prevent weapons on the plane?
The butter knife probably cost Smith no demerits. Arguing about it, and writing about it here, has probably added a note to his file.