What's the ultimate purpose? To subsist using the minimal amount of resources? Have you considered that people may want to eat animals?

Every human activity consumes resources. We cannot make the reduction of consumption as a goal in itself. At the end of the road, what that line of thinking leads to is just existing for the mere fact of existing while occupying the minimal space and feeding ourselves enough to meet our required daily values. I do not think that is an existence that makes sense.

Going back to "agricultural land use". Much of the land use for raising animals would not become a lush forest if left alone. There's a reason it is being used for animals and not crops.