That people have personal identities is false; they are mere parts of the universe. This is clear upon advanced philosophical analysis, but can be hard to understand for those who haven't thought much about it. An objective and impersonal perspective is called for. For this reason it is rational for all beings to 'act ethically' not only for themselves but also for all other beings in the same universe. For an explanation of why personal identities don't exist, what is relevant for the question of why acting ethically in a collective rather than selfish sense, see this brief essay: https://www.facebook.com/notes/jonatas-müller/universal-identity/10151189314697917

Right now I see this as perhaps the most challenging and serious form of moral realism, so I definitely intend to take time and care to study it. I'll have to get back to you, as I think I said I would before.