Well, I personally take the view that any society that forcibly sterilized 50% of its residents doesn't deserve to continue as a society.
I also don't think Malthus was correct.
Someone insinuated that I'd be ok with Jewish concentration camps if that resulted in a society that survived.
That's a hard question to answer. On one hand, what was done to the Jews was clearly immoral. On the other hand, a society that goes extinct isn't around to argue that it was a moral society. Heinlein noted that survival is somewhat of a precursor to moral behavior.
What we'd like to hope is that the choice between survival and violence against others is a false choice - that there is always a way to both survive and not harm others.
But that may not be the case for all societies in all situations.
It may be that the Native Americans came to the conclusion that you did -- that anything beyond a certain population was unsustainable given the technology level and resources they had available to them.
That may have been an eminently moral choice.
It also means that what they thought doesn't matter today - because there weren't enough of them to defend themselves against an invading society with different ideas.