Originally Posted by ralfp

Money translates to lives (indirectly). Security saves lives and property. Like with most things, the first amount spent provides the greatest return on investment (basic screening, fences, whatnot). At some point the ROI drops like crazy, and you start taking lives by spending more on aviation security. More people will drive (more deaths), more of people's lives will be wasted waiting in line, more money that could be spent on actual lifesaving things (medical care and research, etc.) is wasted, and so on.

The 9/11 attacks cost $120billion in total damage, (reference). If spending $60 billion/year could prevent an attack of this type every two years, it might be worth it.