Body scanners at airports are at best a huge waste of time and money, and at worst a source of cancer causing radiation:

"Ionizing radiation such as the X-rays used in these scanners have the potential to induce chromosome damage, and that can lead to cancer," Agard says.

The middle case is that they are a violation of one of the core principles that the founders of America believed: Eternal Vigilance is the Price of Liberty.

It’s easy to spin the idea of “Vigilance” into a creed that authorizes distrust, paranoia and stringent security measures, but doing so renders the phrase an oxymoron. So, how can we be vigilant and have freedom at the same time?

“They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.” — Benjamin Franklin, Historical Review of Pennsylvania (1759)

via Scientists Question Safety Of New Airport Scanners : NPR