[grunder_advice]

I guess I'm pro-natalist. I do agree with you on the goal of eradicating poverty, although to me that's a goal in itself that does not need to be justified. But I don't agree that all people on earth are fungible, and a birth in Mongolia is the same as a birth is Sydney, Australia.

Your "human achievement" viewpoint is highly reductive. The culture of a place is maintained by it's local population. When you have a low birth rate situation to the point that you need to supplement the workforce with immigrants, that signifies that the local culture is slowly dying. While some mixing of cultures is beneficial, we should also try to perserve our local cultures. We should not turn every city in the developed world into a little NYC.