I'm of the opinion this is security theatre. Just one way among many the government gets to remind you You're In Danger and they're doing everything they can to Protect You From Terrorists. There is no evidence any of these invasive screening procedures do anything to increase passenger safety. While grandma's nail clippers will be confiscated (and her privates potentially fondled), the guy behind her knows how to make a knife in the bathroom from metal epoxy, folded cardboard and a spoon handle. So why are they doing it? A) patronage of the firm that makes the scanners, and B) because they have discovered that not only can they can get away with it - the authoritarian electoral base even approves of it.
Here's the thing though, I think security theatre is a strategy that is likely to be abandoned when the people start to perceive the authorities themselves as a more discomforting security threat than the terrorists, and express that view to their elected representatives in great numbers. IMO, this is getting quite close to that line. Obviously, there will always be some authoritarians for whom NO violation of their privacy by the state is unwelcome, but for the majority I think having their children photographed naked and / or their genitals groped by adults at the airport is over the line. I think these policies will eventually be abandoned, or at least scaled back. In any case, this is one area where I approve of the one airport's decision to use a private security firm, but with caution. There's nothing to prevent private firms (think Blackwater) from implementing the same process.