Slavery being right or wrong, capital punishment being right or wrong, animals don't comprehend such things. You're taking this matter in a strictly human point of view.

"Just because something is a certain way in nature does not suggest anything regarding how things should be."

Who decides what how things 'should' be? That's strictly your (human) opinion. There's no representative from nature that comes down to sign a treaty or something. How can you argue against this??

And human morals don't have anything to do with how nature works. Does earthquakes have anything to do with morals? natural selection have anything to do with morals?

Again, the above points were heavily hominine. We can say or label whatever we want about how the nature works, but it's still a man-made definition that is designed severely parochial and exclusively dependent on human's whim.