If I were a TSA agent, I would be afraid of sitting next to the x-ray machine that we send our carry-on luggage through day after day. Who knows how poorly those things are maintained or calibrated.
But that said, you raise a good point. Here's MY big question--are we even using a valid standard when assessing dose?
If there are any medical physicists out there who can correct this, let me know if my thinking is way off base. The thing about high energy ionizing radiation, like x-rays, is that most of it actually passes through your body without interacting with it. However, in those cases where it does interact with your body, then it is energetic enough to do damage to the DNA and so forth.
However, with the "backscatter" and "millimeter wave" technology that the these "naked body scanners" employ, they often remark that they do no harm because it is all absorbed by your skin and can't penetrate deeper. Uh...well, if our skin is absorbing all of the dose, then we're concentrating that dose in a very small portion of our body. Do we know what the risk of that kind of exposure is? I really don't think so. We don't have any/much experimental or historical data on this type of exposure that I'm aware of to say that "below X dose per time Y" is "safe" for this kind of radiation.
There are some travellers who will be asked to go through the scanner pretty much every time they fly, and if they fly often, I think that's a really big question mark for them.
And do they really make us safer? Just the other day, that undercover TSA agent went through the scanner each time and got through with a gun, what--five times, something like that? If I were a well endowed lady or fat enough to have some substantial rolls, you could hide quite a bit from these scanners.