I cannot imagine what system of ethics you are operating from that you would have to ask this question. The point, always, is to provide the best possible life to the greatest number of people, without regard to where those people come from. My goal in life is to maximize human happiness, I do not care what nation a person is from. Unless I'm misreading your words, or you chose your words clumsily, you seem to want a system that works for some set of people but not another set of people. But I'm curious, one what basis would you chose one set of people, and then why would you care about them at all, rather than care about some other group? If you're not going to care about the happiness of all people, then it seems to me you should be consistent and not care about anyone's happiness. But if you honestly care about one group, but not some other group, I'm curious on what basis you chose the group that you care about? And do you really care about them?
"You're only playing a game of managed extinction in cooperation with your country's new settlers"
I think you meant to write "One generation has apparently found it is possible to maximize their happiness without having children, and now gratefully receives help from new arrivals so as to take care of them during old age, as they have no children to care for them."