Murder is also part of the “circle of life”, whatever that may mean, given that it’s pablum that means nothing. As is disease.
We rightfully find these immoral and don’t engage in them.
That’s not a defense of the immoral act. It’s just words to describe the immoral act.
You skipped a step. Immoral acts are immoral because we deem them so. Animal slaughter in itself is not generally thought as such. Unless you think aboriginal / hunter-gatherer tribes who maintain their traditions are immoral for not modernizing.
Killing is part of the "circle of life". Murder is not. They are two very different concepts.
Try this then: every animal eats other living things to survive. We have been doing it for a billion years. Is a basic drive built into it DNA. After that, is just a question of which living things you are going to eat.