I don't trust them to not save the images, I don't trust them to not get hacked, and I don't want some random black hat to have images of my body over time.
PS: Michael Chertoff, the former Secretary of Homeland Security, represents scanner manufacturers. So the whole thing is a massive conflict of interest if you ask me.
Assuming it's possible to say that two images are from the same person, it would be trivial to work out specifically who that was with any frequent flyer.
You'd just build up a body of images of "person 1" then cross-reference with flight records till you narrow it down to only being one possible person who had been on all those flights...
I hadn't thought about it before you asked, but this would be a perfect way to build up detailed information for biometric databases. You'd then use that with lower-fidelity sources, like video cameras.
You've got head shape, hand shape, height, shoulder width, BMI, and length of every major body segment. From there you can calculate all sorts of ratios to apply to people, and I'd bet you could make a pretty good guess at gait for motion analysis.
A database like this would also be proof against facial surgery; changing bone lengths is harder. So if you get a known terrorist once, you should be able to spot them much more easily in the future. And of course you'd keep the records indefinitely, because you never know who's going to turn out to be a terrorist. Or a drug mule. Or a political protester [1].
You asked a question. I gave you an answer. If you have a problem with that, try breathing into a paper bag for a while and see if that helps you calm down.
This technology could be plausibly misused for security purposes, and then perverted for political purposes, just like previous security technologies/bureaucracies have.
That shouldn't make you upset at the people pointing it out. Instead, direct your outrage at the portions of government that have previously done exactly this sort of thing.
Wiretapping and saving everything in the internet, including comms from allies and neutral parties, is foolishness or possibly a form of mental illness.