The composition of a population matters more than population size.
In ancient times we see a world that was far less populous yet far more violent with lower standards of living. Over time people have been selected to be more productive and less violent even at much higher population densities.
The most casual glance tells us at once that how people are bred, organized, and educated is far more important than numbers alone. A million humans bred for aggression, with no civic organization, and who are illiterate will be far more miserable and short-lived than a billion who can work together in peace.
This is why people who want to help overpopulation by not having kids are misguided.
If they, with their altruistic and cooperative tendencies choose not to procreate, they merely select for those who will reproduce recklessly. Any “slack” that they free up for the species quickly disappears and further breeding is even more reckless.
If anything those who altruistically sit out of the game actually make the Malthusian trap even worse as even the capacity for restraint and long-term planning gets bred out, dooming the race to an eventual precipitous crash of famines, plagues, and wars.
A solution to the problem is to engineer societies to encourage conscientious cooperators to have babies and limit the fecundity of those who are short-sighted and vicious.
It may seem far-flung, but the inability of short-sighted people to plan makes them easily manipulated. Their need for instant gratification means for small gains, more drugs and cash, they’d willingly get sterilized. Thus the traits that make them fit under present circumstances would again, with such a correction, make them less fit.
It requires a certain conviction to make objective value judgments about populations of human beings, yet it must be done because avoiding the responsibility of judging leads to even worse outcomes.
Those who disavow children because of overpopulation are taking the easy way out, assuaging their guilt superficially while avoiding a higher responsibility to oversee the herd.
Of course, anti-natalist beliefs are also a convenient excuse for people to avoid children that will just be drains on their lives, so arguing the point matters little. We all contrive a facade to justify what we want to believe anyway.
In which case, it may simply be that in a world with abundant contraceptives, those who do not have an urgent drive to reproduce independent of sexual lust will simply go extinct, since it isn’t rational for an individual to beget the burden of offspring. Strictly rationally speaking, we live and die one life only, so the fate of a family, tribe, or species ought not to matter to us. Yet just one look at how the universe works shows us rejection of this sort of selfish nihilism is required to thrive and live well. Those who live for their brief day and stand outside the circle of life always lose to those who cooperate with the intent of nature. Anti-natalists, overpopulationists, selfish nihilists struggle against the laws of physics while those who work with ways of this universe succeed without effort.
Even the unusual breed of altruists who wish to reduce suffering by not continuing the cycle any further fail in their goals. By abstaining out of compassion and empathy, they merely select for those without compunction.