Buddhism doesn't shun, it doesn't differentiate - it encompasses everything in its rich vastness.
I have always believed that Buddhism is not a religion. It is more than science of mind: I mean to say that it doesn't only tell us how of many things in our lives but it tells us the basic thing of how to live. I have it in my mind, the desire to really feel the realization of the nature of mind and I feel that this will let me be more moral and this fact reassures me that I won't turn nasty - not in any way.
Why Killing Animals is a Sin
Killing animals is a sin according to me. It is not because Buddhism tells us that it is a sin. It is because, I can feel it inside myself the wrong in it.
1. It is a sin to take lives of other living beings - and it is a simple fact that needs no justification.
2. Humans were not born to make balance in the ecosystem - other animals do that because they are not equipped like humans to have other means.
3. Humans can't be equaled to other animals because humans are animals with brain who can think, judge and assess.
4. Humans don't have to kill animals to balance the ecosystem because what humans can bring through it is already there in the food web. If humans are meant to bring balance by killing animals in the food web, then there should be someone eating humans too.
5. If it were all natural to kill animals, or eat meat, why doesn't someone who does it get satisfaction? Have anyone felt good after killing an animal?
Ask those who feel it is OK to kill animals to kill and rest in some mental discussion with himself. Ask them if they get any satisfaction or peace from that act. Then, probably he will know what it means to kill. Also ask them to contemplate someone killing him and what thoughts he might go through when he sees his murderer before him. Would thoughts be beautiful? Would he think, 'oh here is my death coming. He is gonna kill me and I am glad someone is going to end my life'?