Self-harm isn't moral or amoral, it just is. It's as moral or amoral as deciding if you should or shouldn't eat another animal (yes, this includes humans -- Donner party anyone?).
Life isn't black and white. Where I've landed with this thought experiment through my own meditations and readings is that the universe/reality is a recursive fractal of spectrums within spectrums.
And this is just scratching the surface of this stuff.
2. Who says the living of lives does not repeat over time? Your/our "next" life may start in 300 B.C.
Two things science knows barely something about: consciousness and the arrow of time. The self is only an illusion. Physics has lots of symmetry. Therefore, it would make sense if the universe was fair in the end. So the egg theory actually makes sense, more sense than anything else I've heard actually.
Re 2, yes and in 300 BC you're also expected to already have been 50% alive there.
Your egg can't explain consciousness or the arrow of time either. How is the person in egg limbo, the fetus being developed I mean, conscious? How does the egg limbo work at all? You're gonna need a big hand to wave the (meta-)physics of your little egg universe away.
As for the meta-time thing, functional decision theory [1] solves this. The application is particularly clean because your memories are erased between lives. There's no factor of 2 free lunch from temporal ordering.
Or you've already been said person, in which case it won't harm you anymore. Not to mention that it's inevitable that you will hurt the victim because it already happened from the victim's POV, who you've already been. The egg is in a fundamentally contradictory realm anyway because it's asserting free will and same-universe time travel at the same time.
> the story's premise kinda eliminates our usual ideas about morality
Allowing for psycho maxxing, yes. You can take "I should be a good person" from it, but so far you haven't made a compelling case. There's no reason why you shouldn't be an exploiter in 1-10% of your lives, living off the direct and indirect suffering of the 90%. Kind of like within a modern life you can choose to suffer 90% of the time (work, gym, studying,...) to get a halfway decent 10%.
Is self-harm ok? What could be considered good about it?