Interesting observations. Yes, this is getting a little too OT. I will say that I've been having these discussions for many years regarding synthetic races that are, effectively, individually immortal. What is their motivation to self-sacrifice? GC dodges around this with the wholly unconvincing assertion that the (good) Arnor "do not experience time". That dog don't hunt.
The willingness to die for one's offspring, I could see the possible biological component to it. But not self-interest.
Darwin would suggest otherwise. The highest form of material self-interest is that one's genes survive. It's almost difficult to call it altruism.
The Greeks had a ball with this topic, e.g. agape vs. eros.