Nonhuman animals are integrated with human "monkey spheres" - e.g. people live with their pets, bond with them and give them names.

A second mistake is that you decry normative ethics, only to implicitly establish a norm in the next paragraph as if it were a fact:

I, like you and everyone else, have a monkey-sphere. I only care about the monkeys in my tribe that are closest to me, and I might as well admit it because it's there. So, nevermind cows and pigs...

Obviously, there are people whose preferences include the welfare of cows and pigs, hence this discussion and the well-funded existence of PETA etc. By prescribing to a monkey-sphere that "everyone" has and that doesn't include nonhuman animals, you are effectively telling us what we <i>should</i> care about, not what we actually care about.

Even if you don't care about animal welfare, the fact that others do has an influence on your "monkey-sphere", even if it's weak.

Btw, aren't humans apes rather than monkeys?