Asaalamu alaikum everybody,
A few days ago a non-Muslim friend of mine asked me to explain Eid ul-Adha to her. I tried my best, but she was deeply upset by the idea of sacrificing an animal. I explained the story behind it, but she was greatly disgusted. She called it "barbaric and inhumane." Naturally, I am disappointed about this and I do not want her to see Islam as a barbaric religion. How can I explain this so that she will understand better?
Jazak Allah Khairan for your help
Peace and blessings be with you all
Well sister, if she's a strict vegetarian, then I believe she is also a Hindu or Buddhist or similar, Aryan religion follower most probably.
If she is a Hindu, do tell her that animal sacrifice, specially a cow, or any animal, is not banned in Hinduism. It was taken from the other Aryan religions and added into Hinduism recently.
The Vedas, highest scripture of Hinduism doesn't speak anything about animal slaughtering being wrong.
Now the reason why she is a vegetarian and dislikes slaughtering of animals, it is because... ->
Hindu scholars have a philosophy or they believe in something called Samskara. They believe that every human being, aka, every soul, after they die, they are reborn. If you do good in this life, then you are reborn to a higher level, if bad, then lower level. Human being is the highest level and you are born as a human being 7 times. So if you do wrong, you may sometimes be born as a cockroach, sometimes a rat, sometimes a cat, a dog, a monkey, a donkey, a human being, anything, any living being.
The reason why they believe it is because, Hindu scholars, they weren't able to answer, why are some people born poor, why some rich, some sick, some with congenital heart disease, and so on. So they made a theory, they themselves discovered, they say, that because you did a mistake in your previous life, so you are born sick, poor, handicapped. And like I said, you do wrong, you become a lower animal, like a cockroach, a cat, a dog or something similar.
But I find a major flaw in this logic.
Is the human population increasing or decreasing?
But natural increasing.
Is the crime rate increasing or decreasing? It's increasing.
So the theory says, if more bad things happen, then less human beings, aka, more sins, less humans, more humans, less sin, but this is not the case. It's totally opposite

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Tell her this.
Secondly, they talk about universal brotherhood. Like I said, everything is your brother, a cat, a dog, a lion, all, every living creature is your brother.
If you ask a doctor, he will tell you, if this is the case, then we human beings are killing millions of our brother every second. You know how? When you breathe, in your nostrils, there are cilia which blocks the germs and kills them, and helps you stay alive. So your friend, if she hates killing living things, ask her, why does she kill millions of her brothers to stay alive every second?

.
Now last point, the way slaughtering is done in Islam, the animal doesn't feel pain at all. The swift cutting of the vessels of the neck disconnects flow of blood to the body and the receptors responsible for pain, they stop working and the animal doesn't feel pain. The animal jumps, whirls, and struggles, not because of pain, but because of the muscles of its body starving of oxygen.
If you understand advanced biology sister, you will come to know, that whenever there is oxygen deficiency to any part of the body, the aerobic respiration changes to anaerobic respiration. When anaerobic respiration, in lack of oxygen takes place, then many reactions such as actin-myosin, tropomyosin, and many reactions take place which stretches and relaxes the muscles. Hence the animal seems like it's struggling in pain, but that's not at all the case.
I hope this mini lecture helps

. God bless.