I think this is runaway philosophizing where our desire to believe something coherent trumps what types of beliefs we have been selected for, and the types of beliefs that will continue to keep us alive.

Why should I believe what humans have been selected for? Why would I want to keep "us" alive?

I think those two questions are at least as begging as the reasons for my view, if not more.

What I know for sure is that I dislike my own suffering, not because I'm sapient and have it happening to me, but because it is suffering. And I want to do something in life that is about more than just me. Ultimately, this might not be a "more true" reason than "what I have been selected for", but it does appeal to me more than anything else.

Why should there be a normative ethics at all? What part of rationality requires normative ethics?

All rationality requires is a goal. You may not share the same goals I have. I have noticed, however, that some people haven't thought through all the implications of their stated goals. Especially on LW, people are very quick to declare something to be of terminal value to them, which serves as a self-fulfilling prophecy unfortunately.

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.

I discovered that intuitions are easy to change. People definitely have stronger emotional reactions to things happening to those that are close, but do they really, on an abstract level, care less about those that are distant? Do they want to care less about those that are distant, or would they take a pill that turned them into universal altruists?

However, it protects me and my monkey-sphere if we can all agree to keep expropriation and force to a bare minimum and within strictly prescribed guidelines.

And how do you do that?

So I recognize the rights of entities capable of retaliating and at the same time capable of being bound by an agreement not to. Them and their monkey spheres.

If a situation arises where you can benefit your self-interest by defecting, the rational thing to do is to defect. Don't tell yourself that you're being a decent person only because of pure self-interest, you'd be deceiving yourself. Yes, if everyone followed some moral code written for societal interaction among moral agents, then everyone would be doing well (but not perfectly well). However, given that you cannot expect others to follow through, your decision to not "break the rules" is an altruistic decision for (at least) all the cases where you are unlikely enough to get caught.

You may also ask yourself whether you would press a button that inflicts suffering on a child (or a cow) far away, give you ten dollars, and makes you forget about all that happened. Would you want to self-modify to be the person who easily pushes the button? If not, just how much altruism is it going to be, and why not go for the (non-arbitrary) whole cake?