That's not the problem: a Nigerian emits 5% of the carbon footprint of a US person. So they could have 20x as many babies as the Americans? We also have wide differences in the same town and family, too: for instance, my father has emitted at least 20x the CO2 than I did in 2020 (because he like big cars, big houses and fly many times a year).

The problem is clearly what each human being can emit for themselves, according to their means.