...and then we'll all take a look at the animal kingdom and see that Chimps and Dolphins and all sorts of species treat each other - and other species - with innate brutality, and realize this planet is simply one giant cage match.
The point isn't how they treat each other necessarily, but how we treat them in light of the knowledge of their "individual" characteristics, not unlike human beings. So we humans then extend the gift of life to other species.
Those animals treat each other as a matter of survival, is it necessary for us to do the same?
Any cat owner has observed this behavior.
But, yes, animals often produce suffering. In fact, they've been doing it for a while before we got here. But animals are largely doing it out of instinct, not because they've reasoned out and concluded that it was the "right" thing to do.
a) that which justifies doing as their instincts say
and
b) that which justifies acting in their interest as determined by their instincts.
Humans are animals. We happen to possess an extraordinarily tool for abstract reasoning. That tool is mostly used for rationalization and not as an oracle of truth. We are all creatures of biology. Most everything we do is about getting food, shelter, performing sexual displays, and various forms of social signalling and jockeying.
We have all sorts of conmen that market it all sorts of bogus ideas, even the ideas of food is bogus, and entirely irrelevant to the survival of this body.
It is the attachment to the pleasure movements that motivate us, but more fundamentally the attachment to the thought structure, and demand the repetition of various kinds of thought that has produced the human being, and at a very basic sense our selves as we know it.
So it is the thought there that has demanded continuity, and in that continuity you have a plethora of varieties that add to the momentum of that thought, and this is the case with all things, from scientific, to the so called "artistic", to the religious.
What is religious thought other than the demand for ultimate pleasure without a moment of pain, to have compete happiness, bliss, without a moment of another, which is in itself a bogus idea.
So the ultimate question then isn't really a question at all it is really an answer, as then the only thing left is what we demand in thought.
So then what is it that you demand?
I personally see no reason to kill anything at all for the satisfaction of this body, nor do I see any motivation to purposefully torture animals, but if that is what you do then it is up to you, but basically it is not required, and is only demanded by that repetition of thought.
It is interesting to ponder what the nature of other animals is; discover what possibilities we have in common with them. That doesn't change that humans are capable of self examination and choosing between cruelty and tenderness, empathy and callousness.
There is no boundary between nature and other things, nature is all encompassing. There is nothing in nature that can be indifferent because nature can't be different from anything.
Sounds like we could use some rats