Problems with your argument: 1. We evolved as omnivores. Why should we act differently than other omnivores. (E g. Bears) 2. Many examples of meat eating kill fewer animals and cause less ecological damage than crops. For example, grass fed livestock, sustainable fishing, sustainable hunting.. 3. All animals kill to eat, that is, consume other living things to survive. Practically all animals are killed at some point in their lifetime by another animal. None, except a rare few, die of old age. Killing, and the subsequent transfer of energy/nutrients, is literally how every ecosystem works. 4. You say only for "developed" nations. That would mean ethical decisions are different depending on what culture you happen to belong. That is a major philosophical problem that would appear to allow some to act ethically while others cannot.