Standing behind the BriarPatch Co-op Community Market's meat counter, 28-year-old Marc Mongiardo appears to be an ordinary grocery store butcher " though his lifestyle is guided by a philosophy of excluding the use of animals for food, clothing or any other form of consumption.Mongiardo is a vegan."Being a vegan requires less energy to feed than it takes to feed someone who eats meat," Mongiardo said, eating his lunch of fresh garden greens. "It takes more resources to raise a cow versus growing beans and vegetables. On a global level, being a vegan helps conserve energy. On a personal level, I …