BTC - Welcome. The TSA is embarking on a body content capture of what's on your hands. The rest is up to you. If you don't care - they won't either. However, just remember you don't actually have to be a criminal anymore to be treated like one in America. The litmus test for any organic test that arbitrarily collects body samples in a body content capture campaign is a simple question: WHAT ARE YOU GOING TO DO WITH THAT INFORMATION?
Have you ever had a bag "randomly" selected for supplemental screening after pushing it through the X-ray? In addition to the manual search, agents often swipe your bag with a clean cloth and put the material into a shoebox-sized detector. They're checking for the residue of bomb-making material -- potentially undetectable by eye but sniffable by the robot.
That same residue will stick to your hands if you're not careful, which is what the TSA is hoping to identify in their random hand swabs. It's just speculation, but our guess is that the underwear bomber had traces of PETN on his hands, so the TSA now thinks that they can foil plots better by checking those members.
Provided, that is, that they swab the right person's hands. As with many of the TSA's initiatives, this new hand-swabbing effort is a random operation, so if the perpetrator gets lucky and doesn't get swabbed -- well, then the problem moves onward.