No one is saying fields of corn and soybean wouldn't exist, but we would have far less of them without animal agriculture. You are creating a false dichotomy of "sustainable"/"not sustainable" the reality is human societies would be much more sustainable without animal agriculture. More sustainable does in fact result in less extinctions/ecosystem impact and reduced climate change.
Maybe I'm wrong but reading your comment it feels like you are letting the perfect be the enemy of the good, and you use your conclusion that we will never be sustainable as your excuse to continue to eat animals.
Maybe I'm wrong but reading your comment it feels like you are letting the perfect be the enemy of the good, and you use your conclusion that we will never be sustainable as your excuse to continue to eat animals.