Barely a day goes by without news of the latest public health threat from the American media. Some of us are told we live in a -cancer cluster--an area with a disproportionate number of cancer deaths. During the summer months, those who live in or near urban areas are bombarded with daily smog measurements and air pollution alerts. City water supplies are frequently called health hazards. At times, it seems as though virtually everything we eat and drink is denounced as bad for us by some -public health expert.- Our cars burn too much gasoline; we own too many firearms; we are too fat;...