Privacy issues are another matter. They are a concern. These scanners produce detailed images of your body -- very detailed images. Some might call them R-rated. This has been passengers' concern. It also has the attention of Congress, which is why Congress mandated special scanner software to make these images more generic and less embarrassing.
Note that the company that makes the backscatter machines could not meet the software deadline, so its contract was not renewed. This means that the backscatter scanners are now history, at least in airports. The Transportation Security Administration (TSA) was supposed to replace them all with millimeter wave machines as of June 2013.
For Medicine Matters, I'm Dr. Sandra Fryhofer.