When I took the course I mentioned in my post above, the explanation was along these lines: when you want to check someone who carries a bag, you need to remember that he has certain expectations about the safety of his belongings. If you're in a public place, it's reasonable that you never remove the belongings without assuring the owner that they are safe and well-guarded. So when you stop a gang of half-drunk teenagers on the street, you don't ask them to drop their backpacks on the sidewalk and then go ten yards further to search them. You ask them to leave the backpacks in a single place, right near them, and while your colleague searches the backpacks, you keep an eye on the dudes.

That's the common-sense thing to do: no one would let their bags two meters away from them in an airport, even if they kept a constant eye on them. You can't just expect someone to be okay with leaving them god knows where.

If you ask people to put their belongings away in a designated area, the correct thing to do is to have that area placed well away from any passers by and a guard near it. That way, you can tell the owner something along the lines of "Please put your bag in that bin over there; don't worry about it, it won't be stolen -- that man staying guard there isn't leaving, he's there to make sure you get it back just as you left it. We need to ask you a few questions, and then we may have to search your bag. we'll search it in front of you to make sure no one steals or breaks anything, and if all checks out okay, you're free to go. Any questions before we start?"

As our instructor mentioned it, it's really important -- especially in places like airports, concert arenas and whatever -- where you might expect one terrorist every two years and ten thousand disoriented folks with a scare of flight who triggered the bomb detector with their cheap after-shave every day -- to treat people without hostility, with an attitude of collaboration, not suspicion. Very few travelers are at fault for the US' foreign policy (and those that are probably don't go through the whole TSA hell), so it's not their fault that some guys from the Middle East want to blow up their planes. In places like these, you want to treat people so that they can say "yeah, I know this is inconvenient, but the guy is only doing his job", and because they are already under a lot of stress, you want to make sure you don't heighten their fear.