Just a friendly reminder, courtesy of my father, who spent more than a few years cuddled up to a high-output nuclear reactor and more than a few nuclear weapons:
“Backscatter scanners” now used at airports all over the country employ x-rays, which are a form of ionizing radiation. Worse, bystanders/onlookers are not shielded from these devices (just look at them), and thus will be receiving doses of radiation whether they go through the machines or not.
To be certain, we expose ourselves to ionizing radiation on a daily basis – stepping outside, going to the dentist/doctor, flying on a plane (especially flying on a plane, given your altitude), etc. However, every exposure to radiation should be kept to a minimum, and is experienced as part of a larger cost-benefit analysis: is the danger to you from that dose of ionizing radiation smaller or greater than the danger posed to you by starving if you never go to the grocery store, or a cavity, or a broken limb, or not visiting your parents over the holidays?
And bear in mind the second conclusion from the above-linked report:
Even exposure to background radiation causes some cancers. Additional exposures cause additional risks.
So, tell me: even discounting the invasion of privacy, even ignoring the infringement of the Fourth Amendment, even ignoring the absurdity of it all; is threatening the health of millions of American citizens an acceptable cost for the “benefit” of a “security” system that does not even perform as advertised?