Smoking is a dangerous habit. One-fifth of all deaths in America—400,000 each year—result from smoking-related illnesses. Smoking causes 85 percent of all lung cancer deaths and contributes to one in five of all newly diagnosed cases of cancer. According to the U.S. Centers for Disease Control and Prevention, more people die from cigarette smoking and its related illnesses than die from AIDS, alcohol, traffic accidents, illicit drugs, murder, and suicide combined.

Considering these frightening statistics, it is difficult for many nonsmokers to understand why anyone would smoke. From the outsider’s perspective, smoking seems unpleasant, dirty, and pointless. As the eighteenth-century writer and critic Samuel Johnson said, “Smoking ... is a shocking thing, blowing smoke out of our mouths into other people’s mouths, eyes, and noses, and having the same thing done to us.”

But smoking offers some benefits: It provides...