The TSA scanners are presented to the public as a tool for detecting weapons and other contraband, but I think this is actually a secondary goal and a bit of misdirection. Think about what those scans actually are.<p>They're biometrics. They take precise measurements of a person's shape, which is sufficient to detect if someone is traveling under a false name, and they're building a database of those biometrics to have available for use elsewhere. If the scan's result is ambiguous, they swab your hands and stick the swab in a machine, supposedly to detect residue from explosives but with the nice side-effect of producing a stored DNA sample for later use. They've proven pretty useless for controlling the flow of contraband, but they're quite useful for catching fugitives. While the people staffing the checkpoints aren't particularly smart, it's reasonable to assume that the people at the top are pretty clever, and their policies are consistent with this having been the real goal all along.<p>If they tried collecting fingerprints from travelers, they would get a very strong backlash. This way, they get a weaker backlash and some jokes about how stupid they are for using machines that can't reliably detect guns.