Bouncing Ball,
Great posts. I agree, but I'd like to suggest two additional things to consider about our ethics:
1) Cooperating, helping, and giving to others makes us feel good. It makes us feel good even if our actions are not in our "self-interest", narrowly defined. We don't need to justify this feeling because we don't have a choice in the matter: the feeling comes from how our social mammalian brains are wired. The irresistible feeling of satisfaction that we get when we feed/nurture/entertain a small child is sufficient to motivate these actions and call them "good" without having to justify how they further our personal, narrow self-interest.
2) At the same time, it is possible, through education and practice, to train oneself to automatically feel good when one does certain (good) actions and to feel bad when one does certain (bad) actions (or when one has good/bad thoughts). We could use this power to raise children who love nothing more than to murder and steal from each other. Or, we could use the malleability of our brains to raise children who are appalled by murder and stealing, and who derive great joy from helping and cooperating. Clearly, the latter option will lead to greater happiness and less suffering for both the individual AND the group.