Behavior detection works but under certain circumstances. This also means that it will not work in other circumstances. The line at the airport, IMHO, is one of those "other circumstances."
When I worked as an intelligence officer with sources, being able to detect deviation in behavior was absolutely critical. It spelled the difference between running a reliable source and detecting someone who had been "doubled" by the other side. And when I worked as an intelligence investigator, being able to detect behavioral characteristics in witnesses, suspects and sources was also absolutely critical to a successful investigation. And in those instances when I interrogated refugees and/or prisoners, again, behavior detection was a critical skill. None of this applies at the checkpoint (although I still use certain techniques whenever I deal with both passengers and screeners
).
At the checkpoint, I don't see the rationale behind using behavior detection as an exclusive screening methodology. Now I do see the application of certain behavior detection techniques in the regular screening process, but that's in conjunction with standard screening procedures. For example, hand-wanding an individual who appears excessively nervous; however, if that individual clears the hand-wand and limited pat-down, then, from a strictly screening perspective, there's no need for further action.
So if I detect that someone is displaying suspicious behavior while waiting in the line to the checkpoint, that person is going to be screened regardless of whether I think that person is suspicious or not. And while subjecting them to the additional screening of SSSS may be a solution, in my mind, all we're doing is screening the person twice even if they've successfully been screened the first time. (For those who don't know, I'm opposed to the SSSS methodology.)
I see this BDO concept as "spooking up" what should remain a straight-forward, uncomplicated and simple screening process.