Charles Kenny has an excellent piece in Bloomberg BusinessWeek about security:
The attention paid to terrorism in the U.S. is considerably out of proportion to the relative threat it presents. That’s especially true when it comes to Islamic-extremist terror. Of the 150,000 murders in the U.S. between 9/11 and the end of 2010, Islamic extremism accounted for fewer than three dozen. Since 2000, the chance that a resident of the U.S. would die in a terrorist attack was one in 3.5 million, according to John Mueller and Mark Stewart of Ohio State and the University of Newcastle, respectively. In fact, extremist Islamic terrorism resulted in just 200 to 400 deaths worldwide outside the war zones of Afghanistan and Iraq—the same number, Mueller noted in a 2011 report (PDF), as die in bathtubs in the U.S. alone each year.
…According to one estimate of direct and indirect costs borne by the U.S. as a result of 9/11, the New York Times suggested the attacks themselves caused $55 billion in “toll and physical damage,” while the economic impact was $123 billion. But costs related to increased homeland security and counterterrorism spending, as well as the wars in Iraq and Afghanistan, totaled $3,105 billion.
Matt Yglesias adds a good point:
Something that I would love to see the Transportation Security Administration, the FBI, the CIA, and whoever else do is pull together an estimate of how many airplanes they think would have been blown up by terrorists if there was no passenger or baggage screening whatsoever. One way of thinking about it is this. If commercial airplanes were no more secure than your average city bus, planes would be blown up as frequently as city buses—which is to say never. I’ve heard some people postulate that terrorists have a special affection for blowing up planes, but I’m not sure that’s right. In the not-too-distant past, Israel had a substantial terrorists-blowing-up-buses problem and had to take countervailing security measures. But unlike Israel, we’re not doing anything to secure our buses. It’s at least possible that nobody blows up American buses because nobody is trying to blow anything up.
I would also add to the monetary costs the price of lost civil liberties and a populace that has sadly grown accustomed to government surveilling, scanning, and groping. As I said some years ago when visiting Independence Hall, the price of eternal vigilance is liberty.