So what's the solution? Condoms?
Condoms, the pill, education, people who make a career out of being welfare moms, and ending tax breaks for having kids. Easier access to abortion procedures would help too, as well as mandatory sterilization of people with severe congenital defects and career criminals.
But most importantly, stop the Cult of Pregnancy = good. The simpering glorification of babies as something amazing, special, rare, precious, and wonderful. That the simple act of breeding is some sort of special form of qualification for sainthood, something we must pay homage and deference to. Perhaps if society didn't make it so darn attractive, people would have less children.
The US birth rate is not very high at around 2 kids per woman--not as low as Europe but nowhere near as high as India, Latin America or Africa. Increasing numbers of US-born couples are imitating Europeans by having no children at all. Very few people think that raising a large family on welfare payments is an attractive lifestyle, and poor people are not the huge consumers of the planet's resources.
Large families are just not viable in urban industrial societies where everything costs money and kids stay dependent into their 20's.
People have lots of kids in places where babies die a lot, kids bring in income, women have few rights and people must support their elderly parents in the absence of old age benefits.
Worldwide, people voluntarily have fewer children when they have good social welfare policies, so they don't feel the need to have many kids to ensure basic survival.
People need assurance that they won't fall into utter poverty, a guarantee that their kids will survive infancy, and security for their old age. Opportunities for women and girls other than raising the next generation is also important. Then people can have one or two kids instead of 6-8.
A stopgap social policy (that can not be implemented for obvious reasons) would be for every first world person to adopt two kids from a poor country instead of having their own. Then the poor family would know that at least two of their kids would survive, and the first world people could have their cute babies.
But even that would only be a temporary solution, because adding more people to the first world will destroy the planet even faster. The most reasonable thing would be for first world people to help support kids in the third world so that they can stay in their low-consuming countries.
But that ain't going to happen either. Sigh.