Not long ago, I stood outside a closed-down slaughterhouse in Chino, Calif., with Wayne Pacelle, the first vegan to become president of the Humane Society of the United States — he hasn’t put butter on his rolls or poured milk in his cereal since he was a 19-year-old Yale undergrad. He tugged on the locked front gates of the slaughterhouse and called out to a security guard who sat unresponsive behind mirrored sunglasses in a small hut. Then, walking along the perimeter of the plant, Pacelle discovered a low brick wall, and he and I climbed on top. From there we could see the open-air section of the plant and its acres of quiet concrete. The trucks that once arrived at all hours of the morning and night, loaded with cows, were long gone. The pens that held the cows as they awaited U.S. Department of Agriculture inspection were empty. The slaughter chute that once moved about 500 cattle a day into the “kill box” sat motionless.