I generally agree with your view, but to play devil's advocate: The birth rates have been below replacement rates in developed countries for quite some time no

I generally agree with your view, but to play devil's advocate: The birth rates have been below replacement rates in developed countries for quite some time now. If the 50 million humans were happy people living in abundance and luxury, it may not inherently follow that the population will increase. That said, I'm not sure how one would choose the 50 million or restrict people from having children in a way that isn't dystopic.