How can we stop bank robbers in their tracks? A politician might suggest doubling the number of guards to calm the public and intimidate would-be thieves. A policeman might recommend installing more video cameras, combination locks and metal gates. A judge might advocate increasing legal penalties for armed robbery.

These approaches, though well meaning, would remain tedious, expensive and arbitrary; no matter how great our resolve, we simply can't anticipate every threat to every bank in the country. Fortunately, there is another solution, inspired by Willie Sutton's purported explanation of why he robbed banks: "Because that's where the money is." If banks no longer distributed hard currency and became mere financial-service centers-turning over the payment function to smart debit cards-bank robberies would stop.

So far, society prefers to absorb the cost of bank robberies rather than move to a cash-free economy. Yet Sutton's practical observation offers an important clue to addressing a challenge that our society does judge intolerable: terrorism. The most effective way to address terrorism is neither better offense nor better defense. Rather, it is to take away the ball. Creatively eliminate the tools of terrorism, and you go a long way toward eliminating the terrorist.