There's no denying that a collapse in stock prices today would pose serious macroeconomic challenges for the United States. Consumer spending would slow, and the U.S. economy would become less of a magnet for foreign investors. Economic growth, which in any case has recently been at unsustainable levels, would decline somewhat. History proves, however, that a smart central bank can protect the economy and the financial sector from the nastier side effects of a stock market collapse.