What boosts a firm’s stock price, and the boss’s standing, is a rapid expansion in revenues and market share. Privately, he may harbor reservations about a particular business line, such as subprime securitization. But, once his peers have entered the field, and are making money, his firm has little choice except to join them. C.E.O.s certainly don’t have much personal incentive to exercise caution. Most of them receive compensation packages loaded with stock options, which reward them for delivering extraordinary growth rather than maintaining product quality and protecting their firm’s reputation.

Limiting the development of those securities would stifle innovation, the financial industry contends. But that’s precisely the point. “The goal is not to have the most advanced financial system, but a financial system that is reasonably advanced but robust,” Viral V. Acharya and Matthew Richardson, two economists at N.Y.U.’s Stern School of Business, wrote in a recent paper. “That’s no different from what we seek in other areas of human activity. We don’t use the most advanced aircraft to move millions of people around the world. We use reasonably advanced aircrafts whose designs have proved to be reliable.”