Reflecting on the tenth anniversary of the tragedy that has helped define the early 21st century gives us an opportunity to evaluate our response and to identify constructive steps going forward. The simple fact has been that a lot of what has been spent on Homeland Security has been wasted. Colorful rhetoric to the contrary notwithstanding, terrorism does not pose an “existential threat” to the American way of life. The sooner we realize this, the sooner we can quit wasting resources on projects of dubious benefit.

In the third installment of a three-part series for Slate (1, 2, 3), security experts John Mueller and Mark Stewart estimate that even under very charitable assumptions about the effectiveness of Homeland Security measures, current levels of Homeland Security spending would have to stop 1,667 major attacks on the scale of the failed 2010 Times Square bombing every year for the benefits to justify the costs.

Mueller and Stewart put the probability of an American being killed by a terrorist at about “1 in 3.5 million per year.” In this Regulation magazine article, Mueller notes that the American death toll from terrorism is comparable to the death tolls from “lightning, accident-causing deer, or severe allergic reaction to peanuts.”

Mueller and Stewart also estimate that to reduce the risk, we’ve incurred about $1.1 trillion in both direct costs (spending by governments at various levels plus the private sector) and indirect costs (insurance, passenger delays, additional highway deaths, and lost gains from trade). Are the benefits worth the costs? Almost certainly not: we are incurring enormous costs to reduce risks that were already very, very small.

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