One argument often made against taking significant actions against terrorism is that the number of people killed or injured by terrorism is, by comparison with other causes, extremely small. So even 9/11, which resulted in the death of nearly 3000 people, was a mere fraction of the approximately 35,000 people who die every year from car accidents. The idea seems to be that we should be spending much less money on preventing terrorism, perhaps no more per life saved than we do for each life saved from car accidents. That we do not do this suggests a severe innumeracy of…