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If it is so horrible to eat animals, why is it ok for animals to eat other animals? What is different between animals and humans that it is ok for animals to eat meat, and not ok for humans?
That is the ring finger of the moral hand. Briefly put: you and I and all primates don't need meat in order to survive. So if all beings who do not need meat stop eating meat, those populations would no go extinct and biodiversity would not decrease. But a lion needs meat. So if a lion is not allowed to hunt and eat, then no animal is (apply the thumb principle of rule universalism to the ring finger principle), and then all obligate carnivores would die from starvation and then biodiversity decreases a lot. Now we can democratically decide how much moral value biodiversity should have. I want to give it a lot of value, and therefore my ethic says that predation by obligate carnivores is permissible.
Biodiversity (How is this existentially significant?) could still be reduced by economic activities (e.g., the destruction of habitats for the exploitation of their resources).