The world is overpopulated.
Overpopulation is a function of how many people a certain region can support at a certain standard of living; by this metric the developed world is the least overpopulated part of Earth.
In the same sense, we've yet to hit peaks of any significant resource. Scarcity is dropping across the entire world, be it water, energy or food.
Better to have a country of 10 million living in absolute comfort enjoying the benefits of ever increasing automation, than a country of 100 million where most are poor, a detriment to the environment and a threat to human survival.
That's a false dichotomy. You can have a large, productive population that, thanks to technology, is not dependeant upon of the environment regardless of its state. What we're seeing here is the opposite of that. The fertility rate required for population replacement is 2.1, anything under that and you'll see contraction and demographic collapse. And once this collapse begins, it's not going to stop at whatever amount of people hippies believe that "Mother Earth" can carry unless the underlying reasons why people are not reproducing are addressed. It's a perfect example of a tragedy of the commons.
At the end of his book
Apex, the transhumanist novelist Ramez Naam wrote:
“This is about people power, Dr,” she said. “You told me once this century’s most vital raw material is the human mind, did you not?”
Lakshmi Dabir nodded again.
“Good,” Ayesha Dani said. “Because we seem to have more of those than anyone. Now go unlock them. This will be the Indian Century.”
This is not meant to be a cautionary tale about how the poor, foreign masses in developing countries are going to make us irrelevant. That process is already in motion, we couldn't stop it if we wanted to and I for one don't believe we should; it's a good thing.
What it should bring to mind is the fact that the human brain is a
resource
and having more of them is a boon, even if the byproduct of producing the handful one minds that will drive technological progress is hundreds of thousands of less productive ones. A large population is a boon in the long term, not only for any specific country but for humanity as a whole.