The reason the TSA uses these devices is not for our protection, but because Rapiscan Systems wanted a billion-dollar contract to sell these devices to the TSA. The TSA Director was the subject of a lobbying initiative. And that's how our government works. It's also the #1 reason why our government is so expensive.
The TSA is out of order. The fourth amendment of the US Constitution prohibits unlawful search or seizure without a warrant or probable cause. An old lady taking a ride on an airplane does not constitute "probable cause". But the law is somewhat flexible. Putting our personal items through a metal detector is acceptable. Removing our shoes is stupid, but I'll let that slide as well. Causing security to take twice as long just so people can stand in front of a backscatter X-ray is not acceptable. TSA personnel like these devices is because most are barely-literate perverts who think they will get to look at naked ladies. (Rapiscan is a fitting name) The pat-downs sometimes take a long time and sometimes do not. I have only seen female TSA guards pat down female passengers.