I'd say your claim of no health risk is premature. Backscatter X-ray focuses the ionizing radiation on the surface of your skin and immediately underlying tissue, so the effective local dose on your skin is much higher than other types of X-ray which are distributed evenly throughout your body. This is of particular concern to men, whose reproductive organs are located near the surface of the skin, as X-ray exposure to reproductive organs in parents is associated with leukemia in their children. For medical X-rays, measures are taken to limit exposure to reproductive organs.
For families with children, I've noticed that most airports (I've been to anyway) now have a family security line, which uses traditional metal detectors instead of body scanners and doesn't try to make kids go through the scanners. The lines are also usually shorter and friendlier to the extra time it takes getting kids through the line. However, I'm usually slower than the kids because I have to get all my laptops out, belt and shoes off, etc.
If I'm by myself or somehow end up with body scanner as the only option, I always opt-out. I guess part of the theater is designed to embarrass me, but I wonder why I should be more embarrassed than the dude squatting down below me to give me the feel in front of everybody (and no, I don't want a private screening, get down there and feel me up right here in the open). Like someone else suggested, I think they're as embarrassed as I am (or am supposed to be).
