Putting this all together, we find that, in order for the $75 billion in enhanced expenditures on homeland security to be deemed cost-effective under our approach—which substantially biases the consideration toward finding them effective—they would have to deter, prevent, foil, or protect each year against 1,667 otherwise successful attacks of something like the one attempted in Times Square in 2010. In other words, we'd have to foil more than four major attacks every day to justify the spending.
We are not arguing that much of homeland security spending is wasteful because we believe there will be no more terrorist attacks. Like crime and vandalism, terrorism will always be a feature of life, and a condition of zero vulnerability is impossible to achieve. However, the frequency and severity of terrorist attacks are generally very low, which makes the benefits of enhanced counterterrorism expenditures of a trillion dollars since 9/11 challenging, to say the least, to justify by any rational and accepted standard of cost-benefit analysis.
Our findings dealing with the total enhanced homeland security expenditures should not be taken to suggest that all security measures necessarily fail to be cost-effective: There may be specific measures that are cost-effective. But each should be subjected to the kind of risk analysis we have applied to the overall increases in expenditure.
We have done so for several specific measures. It appears, for example, that the protection of a standard office-type building would be cost-effective only if the likelihood of a sizable terrorist attack on the building is 1,000 times greater than it is at present. Something similar holds for the protection of bridges. On the other hand, hardening cockpit doors may be cost-effective, though the provision for air marshals on the planes decidedly is not. The cost-effectiveness of full-body scanners is questionable at best. Overall, by far the most cost-effective counterterrorism measure is to refrain from overreacting.
We have assessed the hazard terrorism poses under present conditions—which include, of course, the existence of counterterrorism measures specifically designed to reduce that hazard. The analysis suggests that additional efforts to reduce its likelihood are scarcely justified.
It is possible, of course, that any relaxation in these measures will increase the terrorism hazard, that the counterterrorism effort is the reason for the low-hazard terrorism currently present. However, in order for the terrorism risk to border on becoming "unacceptable" by established risk conventions, the number of fatalities from all forms of terrorism in the United States would have to increase 35-fold, equivalent to experiencing attacks as devastating as those on 9/11 at least once a year or 18 Oklahoma City bombings every year. Even if all the (mostly embryonic and in many cases moronic) terrorist plots exposed since 9/11 in the United States had been successfully carried out, their likely consequences would have been much lower. Indeed, as noted earlier, the number of people killed by terrorists throughout the world outside (and sometimes within) war zones both before and after 2001 generally registers at far below that number.
We have been using "historical" data here, and these suggest the chances an American will perish at the hands of a terrorist are about one in 3.5 million per year. However, although there is no guarantee that the terrorism frequencies of the past will necessarily persist into the future, there seems to be little evidence terrorists are becoming any more destructive, particularly in the West. In fact, as discussed earlier, according both to official and prominent academic accounts, the levels of violence likely to be committed by Islamist extremists within Western countries seems, if anything to be in decline as fears about large, sophisticated attacks have been replaced by fears concerning tiny conspiracies, lone wolves, and one-off attackers.
Those who wish to discount such arguments and projections need to demonstrate why they think terrorists will suddenly get their act together and inflict massively increased violence, visiting savage discontinuities on the historical data series.
Risk reduction measures that produce little or no net benefit to society or produce it at a very high cost cannot be justified on rational life-safety and economic grounds: They are not only irresponsible, but, essentially, immoral. When we spend resources to save lives at a high cost, we forgo the opportunity to spend those same resources on regulations and processes that can save more lives at the same cost, or even at a lower one. Homeland security expenditure invested in a wide range of more cost-effective risk reduction programs like flood protection, vaccination and screening, vehicle and road safety, health care, nutritional programs, and occupational health and safety would likely result in far more significant benefits to society.