It’s not possible for everyone to have decent living standards. China and India need to decrease their birth rate so the rest of the world can thrive
You may or may not be correct, but I'd say, citation needed.
It's not self-evident that life is such a zero-sum game that more people necessarily means fewer resources to go around; I'd even venture that the last hundred years of development suggests the opposite.
It's quite possible that more people enables a slew of network effects (such as technology improvements due to more minds attacking a problem, say) that improves everyone's living standards.
Tongue in cheek comment about large countries with already under replacement TFR needing to limit emissions when western countries with net immigration are typically elevating consumption of each immigrant to western standards which is equivalent to multiple per capita emissions of world average.
https://www.macrotrends.net/global-metrics/countries/ind/ind... https://www.macrotrends.net/global-metrics/countries/ind/chi...