Yes!!

Exactly!
Ender was set up to show the duality of what we are capable of (the result), but made things ez(ish?) for the cause (high stakes). A few other works "of fiction" (well, basically every sci-fi empire, modeled ofc after non-fiction ones, or even a controlled experiment like in the Rama series) show how are we capable of such duality for much more mondaine causes (petty personal/political/economical interest, even if not really effective or just temporary - one smol personal win over an entire species if practically possible).

But, imho, both is just self-interest (not the unobtainable "objective greater good"), appreciating something when humanity has nothing to wage it against is ez. It just adds to our life experience - much the same way it adds to it to enslave that thing & subject it to horrors beyond imagining for some profit.
Basically Ender looking at it as individual got the best ("most"?) experience he thought he could, didn't he? (I'm not saying it was premeditated.) All the saving/slaughtering and all the saving. I think the duality (def a real thing ofc) is just the entitlement of wanting everything & on our terms.

Eg. on Earth even in the most oppressive slavery regimes you always find stories of how someone "liked" some slave & gave them a """better""" life (only very comparatively to the system they support).
It is the duality of human nature, but bcs both things sum up better for us - if both isn't possible we default to the first one (again, on average/historically speaking).

Tl;dr: yes, duality, but I never understood why there is mysticism around it's existence, it's just that we want as much things as possible & when pleasurable.
We mostly just take ("what we can" being the limit).