Zimbardo showed that the inevitable consequence of unchecked authority is abuse. Milgram showed that a large proportion of us will do just about anything to our fellow man because someone with a clipboard says so. Asch showed us that we will swear that black is white if we are surrounded by people who tell us so.
This isn't about emotion or politics, it is about some basic psychological facts. If you give a man a badge and a hat he will start beating people down the moment you turn your back. If you give a man the authority to do "whatever is necessary", that authority will be extended to dominate and control as far as is possible. If you tell a man "You have no other choice, you must go on", he will kill in cold blood.
All preventable deaths are unfortunate, but deaths due to terrorism are incredibly rare. Even in the most violent and chaotic places on earth, road traffic accidents dwarf the death toll due to terrorism. If we cared about the preservation of human life, we would spend the TSA's budget on eliminating malaria, tuberculosis and infant diarrhea. If we cared about saving western lives, we would spend the money on public health education and support, road traffic safety, school meals and so on.
It is clear that we're not acting rationally. In response to an extremely rare risk, we are spending countless billions on largely ineffective responses and sacrificing civil liberties on a grand scale. This isn't just about body-scanners, it's about extraordinary rendition, warrantless wiretapping, the criminalisation of photography and who the hell knows what else. Whatever argument might be made for the TSA, it is absolutely bogus to suggest that they are in any way a rational or proportional response to risk.
Every dollar that we spend on building scanners or spying on students is a dollar that we can't spend on feeding schoolkids or preventing diabetes or making roads safer. Government spending is finite and every dollar of the TSA's budget is money that could be spent much more effectively and save far more lives.