“Welcome to the Friendly Skies. Now take off all your clothes.”

Don’t laugh! In the wake of the failed terrorist attempt over Detroit on Christmas Day, it may not be long before those scary words greet you upon arriving at the airport, just before you step into the full-body scan machine.

Today, there are only 40 such machines located, and rarely used, in 19 airports across the country. But, spending $25 million in stimulus funds, the Transportation Security Administration has already ordered an additional 150 for 2010, and hundreds more are in the pipeline. Once those scanners are in place, every passenger will be required to pass through one or volunteer to be personally groped in a full-body pat down.

There’s no doubt about it; full-body scanners are a gross and unnecessary invasion of privacy. By stepping into that machine, you might as well take your clothes off and parade naked around the security checkpoint.

TSA officials haughtily pooh-pooh privacy concerns. After all, they reassure us, the agent leering at your naked body is hidden away, out of sight, in a room nearby. So what? He’s still leering at your body. Or your wife’s. Or your daughter’s. In fact, in England, use of full-body scanners is considered a violation of child pornography laws, and the machines are banned for children under 18.

Not only that, adds TSA, rules prohibit agents from storing naked images of passengers or sharing them with friends. Oh, really. After their recent screw-ups in Detroit or Newark, can we really trust TSA on anything?

There’s also the question of radiation. While most experts agree the risk is low – ABC’s Lisa Stark reports that rays from a body scanner are 2,000 times less powerful than a typical chest X-ray – any amount of radiation can increase the likelihood of cancer, which is why many doctors recommend that pregnant women and children, the most vulnerable members of the population, avoid use of the machines altogether.

Despite all those concerns, why is TSA rushing into this unproven and perhaps ineffective technology? Because jumping into something new is how they respond to every terrorist attempt. Only after Sept. 11 did they secure cockpit doors. Only after Richard Reid’s failed shoe-bomb incident did they make us all take our shoes off. Only after the failed plans of British terrorists to mix chemicals onboard did they make us carry tiny vials of liquids and gels in a quart-size plastic bag.

And now, only after a failed underwear incident, do they want us to pose nude for TSA agents. What if it doesn’t work? What’s next? We already know. The latest terrorist plan is to plant explosives inside a body cavity and detonate the bomb with a cell phone. Experts admit that, had Umar Farouk Abdulmutallab done so, no full-body scanner would have picked it up.

So that scary new greeting at airports noted above could get even worse: “Welcome to the Friendly Skies. Now take off all your clothes – and bend over.” A full search of body cavities may be next on TSA’s list of ways to keep us safe. Still want to fly home for Mom’s birthday?

Most frightening of all is the fact that the national security apparatus, with the tacit support (so far) of the Obama administration, is ignoring privacy concerns while pushing universal application of the full-body scanner as the next step in the “war on terror.” As one security expert told me, we have to accept the fact that, from now on, going to the airport will be just like going to the doctor: Once you walk in the door, you give up your right of privacy.

Nonsense. Consider drunk driving. The best way to stop it would be to station a cop outside every bar to test every customer leaving the premises. No matter how much we abhor drunk driving, Americans would never tolerate that – even though drunk drivers killed 11,773 people in 2008. Only 876 people died worldwide in plane crashes.

Same with airline security. We must accept the fact that there will always be risks. The idea that we have to choose between safety and privacy is not only a false choice, it’s a dangerous one. For once we give up even the tiniest slice of our privacy, we’ll never get it back.

Benjamin Franklin said it best: “They who can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.”

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