Forget about the birthers, and the nutty claims that Barack Obama was not born in the United States. More and more, we are hearing from people who might best be described as anti-birthers. Their claims have nothing to do with long- versus short-form Hawaiian birth certificates. Instead, they advance a simple proposition: that the birth of each additional American child is a kind of calamity for the environment. The most recent example of anti-birth thinking comes from Paul Murtaugh and Michael Schlax of Oregon State University. In a study called “Reproduction and the carbon legacies of individuals,” they suggest...