Feed lots are stupid and need to go away, I'll give you that. But turning the world vegan requires turning land that's only good for grazing into farming fields and destroying the natural habitats that already exist. You're also killing thriving ecosystems and killing countless native animal and insect population over and over again and farming until the land goes fallow and that easily creates more deserts.
Every vegan meal in the stores has animal blood on it's hands and is slowly destroying the planet. Grazing, pasture-raised animals have been restoring fallow, crop destroyed areas more to their original native state.