PTTG:
There's a problem.
Humans like to make babies when they feel really comfortable/prosperous.
When your calculus is "X finite resources must be supplied to an uncapped and growing population", the calculus becomes a spectrum, rather than a target, starting at "Everyone gets everything they need and then some" and ending at "Everyone is systemically impoverised when equally distributed-- some people live good while others die of neglect when unequally distributed."
The population growth will level out with resource availablitly, with people living in "adequate but not great" conditions due to increased mortality rates from the lack of resources eventually, but that is in contravention of the stated goal of everyone getting quality needs met.
That is assuming that needs remains a static target as well-- it is not. Energy needs per person has skyrocketed in the past century to astronomical levels.
This is a logistics problem where the premise denies a solution. Modern living is unsustainable, systemically, barring some kind of miracle technology that allows construction and habitations on biosphere-less areas that are not in competition with the natural biosphere, and where all human waste products are perfectly recycled, and where there is infinite room to expand in.
In short, we would need to find a way to produce matter and energy from nothing, then move into outer space.
And yet birth rates are declining despite increasing feelings of prosperity.
The main factor is that quality of life has DIMINISHED-- People have material goods, but they LACK TIME. People spend close to 100% of their time being "Productive", and so, do not spend time making babies, because they are too drained in every capacity to even have sex, or to even contemplate making babies.
Even rabbit populations have an upper-bound where intra-colony stresses cause female infertility.
Again, the stated goal implies quality of life. That is not an attainable target when resources are finite.
This is my interpretation as well. And articles keep appearing at an increasing rate about "Millennials selfishly abandoning family values by not having as many children - future economy doomed!"
Like this one, from bloomberg.
https://www.bloomberg.com/news/articles/2018-05-24/what-s-discouraging-millennials-from-starting-a-familySMJJ:
I really don't need to give every possible aspect of how population growth slows to explain it. I only need to explain enough causality to induce rate to drop below replacement rates. Natural death rates take over from there. Human populations in excess suffer from a resource shortage; Not food, not water, not electricity--- money. Or rather, "value".
As automation, ever more excessive quarterly goals are enacted (Gotta keep that chart pointing upwards for the stock holders!!), and technological rate of development outmodes people sooner and sooner, people spend more and more time and money trying to remain occupationally relevant/valuable, because the thing they have that is valuable is their work. As that work becomes less valuable due to over-availability (due to automation + large population), or due to being obsoleted (due to fast tech revolutions), that resource becomes less available/potent as a means of sustaining a family.
Even in poor countries this is true, as the reward for doing your work is less and less, simply because human life gets 'cheaper and cheaper' as the population grows.
This is the human equivalent of the large rabbit warren. The large population paradoxically supplies a large number of potential mates, but the colony stress levels destroy fertility, until equilibrium at subsistence levels is attained.
AGAIN---
THE STATED GOAL IS TO HAVE QUALITY OF LIFE FOR EVERYONE.
That is mutually exclusive with reaching population equilibrium.