Humans are animals, just like all of the other animals. Animals want to survive. Some do, some don't. Humans are efficient killers. They certainly have changed this planet - often for the worst.
There are degrees of responsibility that we are willing to accept as individuals. That's a personal choice. Farming is often about killing, as well as giving life to things. I'll mercy kill, but not for any other reason. I vowed as a kid watching my step father load up for the slaughterhouse, that I would never do this. The only animals we have are ones who will die on our property of natural causes. I like pork, beef but we will never own these animals because I don't want to be directly involved in their deaths. Our animals are part of our family- once we take it in - we don't turn around and sell it.
This is my way of doing things. I have no problem with others doing as they need to.
I just recognize that every living creature wants to survive as much as I do, cats included!