The vegan argument is a bit misleading because it supposes that all land that is farmed is suitable for cropping and that farming is usually monocultural. Lots of land that is too marginal for cropping can be used to raise animals sustainably and animals can be used as part of a holistic farming approach ie chickens can be used in permaculture gardens, pigs can eat household scraps, sheep and cattle can graze land that is being rotated. Also, in the Australian context, eating feral animals would be a great way to reduce their numbers and farming native animals for food would be far more sustainable than cropping.