* ... because the coiled, closely packed lines at TSA screening sites are the most dangerous places in airports, completely unprotected from a terrorist attack -- a terrorist attack that would serve the same purpose (shutting down air travel) as an attack on board an aircraft.*

This is a good point, but I don't completely agree with it. If terrorists can smuggle a bomb on board an airplane, they can probably smuggle tools on board that will allow them to break into the cockpit. Then (as we've seen), the plane itself can be used as a very large bomb. (Note that I am not venturing an opinion on whether backscatter imagers are a solution to this problem or whether the invasion of privacy is worth it even if they are.)