This is precisely why I choose to opt out. While I do have privacy concerns, the primary problem I have with these machines is the fact that over half of them emit ionizing radiation. Hell, I am paranoid enough to only carry my cell phone on my person once or twice a month and use a corded phone attached to an xlink to talk over it. If I were a TSO at a location with backscatter I would have quit my job.
Dental x-rays are fine - they are but once a year, you have the lead vest on, etc. These backscatter machines scare the crap out of me.