MAGNOLIA, WI — John Adams can’t see the nearly 3,000 cows on the dairy farm two miles from his Wisconsin home, but when the wind blows he can smell them. The stench gives him and his wife headaches. They blame the big farm for contaminating their air and polluting the groundwater well they use for drinking, bathing and watering their garden. They no longer feel safe eating the vegetables they grow. Adams also blames the state, which requires local governments to grant permits to large farms that meet certain limited criteria, even if there are additional environmental concerns. The rural...