It's not that simple. Large herbivores are necessary for many environments and useful agriculturally even if we didn't eat them. Desertification caused by removing trees and grazing without replenishing, nutrients lost because sunlight and wind are scraping the bare soil, monoculture deserts and insecticides killing off pollinators and destroying ecologies... It's the factory farming and profit-motivated short-termist resource extraction that's a problem, not the cows and pigs. We can transition to sustainable methods without decreasing food variety.