Whilst from an academic point of view much of what you say is correct, as an overall global assessment it seems you miss the massive increase in WORLD population, and the corresponding rising demand for resources and 'things', which correlates to our rising energy use and pollution costs.
I am not sure why you see the argument that, at a nucleus level, a larger family may be restricted in the amount of money that can be spent on each child, and the global cost to the family budget of larger numbers of children is greater, hence may be 'poorer' on that basis. In simple terms that is observable in many societies.
There is also the issue of 'equitable' distribution of food and water.... given that control is power, and all countries have those who seek power and control, no matter their government structure, equitable distribution assumes forces that do not exist.
The only way there would be an exception to this would be a world government who intended to create a totalitarian dictatorship, and set 'limits' on the allocation and redistribution of resources, based on population... Is this where your argument is headed?
We have a society, and banks, that worship 'growth' hence the drive towards two income families when growth was not enough with a single working parent (IMF policies) in more 'developed' economies. Our current system stagnates when growth stops (Japan being a case in point).
So despite your noted points we need to address the lemmings progression of world population, and the costs of same, as exponential growth, logically, cannot exist forever with finite resources, and our debt based financial system which is pivotal in modern society fails when growth fails.