Husband and wife environmentalists Denis Hayes and Gail Boyer Hayes take to bashing beef and dairy in their new book "Cowed." Published this year, it attacks animal agriculture on multiple fronts — health and nutrition, food safety and cattle production.

The book also makes one of the most outlandish predictions that you’ve ever heard. According to the authors, "If the human population grows another 50 percent, and everyone starts to eat as much beef as Americans, we will wipe out much of the rest of the animal world."

Ken Cook of the Environmental Working...