Every one of these people are far more exposed on a far more frequent bases to people who can see them up close and personal. Every one of the women spread-em wide for a Gyno typically (hopefully) at least once a year. Men let their balls be cupped by a doc when they cough. Everyone goes through a routine physical at lease every few years, almost or complely naked, with not only a doc who knows them personally in the room, but the passing nurses and staff as well.
Every one of these people are also full willing to strap on a bathing suet, pretty much equally if not MORE revealing on a regular basis, in public.
LOOK at these images. They're gray-scale, faces are blurred, they highlight dense material not identifying skin marks, and are low enough in resolution to see an object, but not the DETAIL of an object. They can't pan, zoom, rotate these images, or focus on specific parts. More over, the people seeing them see then 1) all day long (dunning sensitivity to them), 2) are in another room, where they can not see you, and have no idea who you are, and 3) are looking for DANGEROUS THINGS, not boobies.
So what. Someone who will never see you in person gets to see a slightly more penetrating, but far from superior view of you that any Joe Bob at the beach, and far less than you let your doctor see. These people are forced to see not just your curves you might like to hide, but the curves of people that should be hidden... For every half nice looking (in fuzzy B&W) body that comes through, they're forced to see 50 they'd rather not see.
There's many ways to get around using these scanners: get a far more invasive pat down, get national security clearance levels sufficient to walk right on by, or DON'T FLY! The plane must be secure from terorists. Do you seriously care so much about someone you'll never meet seeing a bad image of you on a screen (and having no association of it to you personally) that you'll risk another 9/11, even when you let a doctor, someone who knows you personally, not only see you, but feel you up and sick things inside you? Get your priorities straight... these people are themselves screened and chosen for these jobs. Trust me, they'de rather not be seeing you this way, but they feel it has to be done.