The answer is that, as we well know from various reports, the body scanners are not 100% effective. That statement is not necessarily a knock - they are supposedly the best technology we have at the moment - it's just a fact. The reason we need to remove our outer layers is the same reason we need to remove our belts: Thick material can prevent the scanners from fully penetrating, running the risk that something on someone's body could pass through unnoticed.
The rule of removing your outer layer at U.S. airports is not as universal as removing your computer or belt, but it is asked of passengers at a majority of them. Next time you're asked to do it right before stepping into an x-ray machine, take a deep breath and understand that you are presumably helping to aid the abilities of limited technology.
With that in mind, if you want ask a TSA agent why they routinely send people who aren't prechecked through the precheck line, we're still looking for a good explanation to that one.
[Photo: CMG Digital]