The problem is how do we even start to evaluate the cost of prevention. Measures? We have equipment and labour costs, that's easy to measure but the data is not made available. But then what is the opportunity cost on those who are inflicted the measures. A person goes on holiday and can perhaps browse a book while queuing for an hour to go through the security checks, a business traveller is simply standing there, unable to even make a phone call due to lack of privacy.
Also, if we spend 1 trillion usd on say the prevention of terrorism, and we "only" suffered 20 death in the United States during that period, it doesn't mean halving the expense would only double the death toll. We put measures and have no tool to measure their effect, high number of variables, and each of their weight evolve dynamically.
I think we better spend time educating the media industry to somewhat control the increasing rate of fear inducing columns published each second. And if they don't learn, regulate them since we are already regulating countless industries for that matter.
Expensive 'raise arms under arrest' full body scanners aren't advertised as opt-in by TSA, but they are voluntary. I always go through standard metal detector only.
Maybe the masses don't care enough about cost/ benefit and allow career beauracrats to run wild designing 'security'.
Did you know the food store workers near the gates walk around TSA screening at most airports? Crazy.