If there is some real reason to be concerned still about the millimetre wave scanners I'd be happy to see some research/evidence to back it up. The only reasonable (I travel pretty frequently, so it's more than once every free months, unfortunately.
[Currently] we have the right to opt-out, no questions asked.
Having to explain yourself eats away at this right. Every time I've opted out so far they've put me in a little pen and then 2 security people have approached me, one with a folder and pen and just making a note of the date, time and the reason.
The same increase also occurs in chronically–stressed animals not exposed to radiation.
Not only is the "radiation" issue invalid, but the privacy issue is also a non-issue.
The updated rule says, "While passengers may generally decline AIT screening in favor of physical screening, TSA may direct mandatory AIT screening for some passengers," (PDF source).