It is not natural to kill animals. Killing and hurting animals contradicts the basic intuition that humans are born with.

You can't prove that it is justifiable to kill animals, or that it is "natural" for us to kill animals.

Killing and hurting animals contradicts the basic intuition that humans are born with.

We have the ability to develop love and compassion for all beings. But it requires that we stop oppressing them. We can intuitively know that it is wrong to cause suffering and to kill another sentient being. However, if we oppress animals routinely as most humans do, we may lose this capacity. Just like persons committing severe moral atrocities may not have comprehended that what they did was morally wrong. I believe that men are goodhearted. However, humans participating in regularly excluding the animals, regularly saying 'I don't care' by the choices made, regularly oppressing them by eating them, wearing them and making other choices that are oppressing the animals, may become very disconnected to the animals, their lives and their inherent moral value.

One can reason like this:
"1. The imposition of suffering on any sentient being requires an adequate moral justification and pleasure, amusement, or convenience cannot suffice as adequate to justify imposing suffering on any sentient being
2. The most “humane” animal agriculture involves considerable suffering imposed on sentient beings
3. As a general matter, our best (and only) justification for eating animal products is pleasure, amusement, or convenience
4. Therefore: We cannot morally justify eating animal products