Now, you can have too few youngsters in the workforce, as a few countries are about to find out.
Could keep the current population AND have a high standard of living WITHOUT it being wasteful: and GOOD NEWS EVERYONE, it's a fun engineering problem! (but it's also a policy problem and requires intentional change) - e.g., reshaping manufacturing away from landfills, agriculture away from crops humans don't end up eating, companies away from stock markets and toward worker control, governments away from lobbyists and towards citizen control....
What percentage of the problem do your greedy, wasteful few pose? I genuinely don't know. What I do know is that the 'greedy, wasteful' ~13% of the earth population (USA+EEA+AU+NZ+JP, 'the western world', is about 1 billion people) forms the vast majority of the problem. I don't remember if it's like 70% or like 85%, but something on that order.
What share of those 1 billion rich people's emissions is caused by your millionaires, I would be interested to learn, but I fear that we can't just push our problems onto someone else, especially that group.
As girls and women got more educated and started to enter the workforce, birth rates declined. This is for one the result of women pushing back having their first child until after they finished their education and progressed into the first stages of their professional career. And secondly, female hypergamy stubbornly persists in modern society. It causes a self-inflicted dilemma for better educated, financially independent women. They find it difficult to find a partner with an equal or better social and economic standing.
Other factors played into this as well, notably the inability to afford property on a single income, requiring both partners to take up work.
I do not believe that there is a silver bullet to any of these problems. The best policy may be to adapt to these developments, rather than trying to change them.
And that number is going to be a function of lifestyle, or quality of life, or what have you. We can support an awful lot of miserable people with stunted growth from malnutrition in sprawling hovels, much more than we can of healthy people in nice homes who aren't miserable with hunger all the time. That appears to be the biggest slider on the carrying capacity formula.
I happen to think that the carrying capacity on the planet is quite low, about a quarter of a billion people. Yes, I am sure some Star Trek tech would raise that. It isn't something you can plan for or count on.
It is currently fashionable to sneer at Malthus, I happen to think that the main failings were his not counting on us finding exciting new ways to burn the future in favor of the present. Yes, we found an awful lot of ways to increase food production, ha ha, here's mud in your eye, Malthus! Now we're starting to wake up to the costs of that.
Thinking we can affect global macro trends like that with policy in one country or another is peak arrogance.
Disinformation.
Most of the world has a negative birth rate https://www.visualcapitalist.com/cp/charted-rapid-decline-of...
2.2 per woman is replacement rate.
https://en.wikipedia.org/wiki/Sub-replacement_fertility#/med...
Most of Africa is replacing their population but they have a higher death rate than many other places.
Everywhere else in the aggregate is negative with a few exceptions.
https://worldpopulationreview.com/country-rankings/total-fer...
Replacement rate in a country with a good health system where people average longer life expectancies is 2.2 births per woman.
Replacement rate needs be much higher than 2.2 in a country with high infant mortality, long wars, etc, such as exists in much of Africa, where birth rates are the highest.
https://www.weforum.org/agenda/2022/04/infant-mortality-afri...
Top 10 Countries with the Lowest Infant Mortality Rate (UNICEF 2020 - deaths per 1,000 live births):
Iceland — 1.54
San Marino — 1.56
Estonia — 1.65
Slovenia — 1.76
Norway — 1.79
Japan — 1.82
Singapore — 1.85
Finland — 1.88
Montenegro — 1.95
Sweden — 2.15
https://worldpopulationreview.com/country-rankings/infant-mo...