The main difference between an inhabitant of India and an inhabitant of the United States is the amount of resources that each of them has available – everything else boils down to that. Resources, in turn, are land. There’s land for food production, land for mining coal, land for dumping waste on so on. Mind that land used by a given coutry does not necessarily have to be in that country, due to global trade. If the UK imports food, for example, then it is using land abroad to feed itself.
The reason that India is able to accommodate the number of people it does is that they live in worse conditions than those in US, so their resource use is low – 0.9 global hectares per capita. For US, this value is 8 global hectares per capita. Now, US economy is known to be extremely wasteful, so let’s take EU (Germany) – the figure there is about 5.
Earth has about 13.4 billion hectares of biologically active surface.
My spreadsheet tells me that India uses 8% of world’s biocapacity, Germany uses 3%, and US uses 19%. Far from overpopulation, right…?
But! Why would people in India always want to live with the conditions they live now? As you have said yourself, they want opportunity. So they will want to develop. And their resource use is going to go up… Say not to US levels (US economy is known to be wasteful), but to German levels. Now, 1.2 billion people at 5 hectares per capita… that’s 45% of world’s biocapacity.
But wait, they will need time to develop, so let’s take projected population figures for 2050 (US - 0.42B, India - 1.6B). If the resource usage does not change, then simple multiplication yields US using 25% of world’s biocapacity. India, with Germany-like economy, would use 60%. So the two, combined, would use 85% of world’s resources for 2 billion people. But wait, we will also have China with its 1.3 billion people… and everyone else of the remaining 8 billion.
So, back to the point I made… Earth can sure accommodate:
- 21 billion people if they live at Bangladeshi levels on average (0.6 per capita)
- 15 billion people if they live at Indian levels on average (0.9 gha per capita)
- 10 billion people if they live at Phillipine levels on average (1.3 gha per capita)
But, it can accommocate only:
- 2.7 billion people if they live at German levels on average (5 gha per capita)
- 1.7 billion people if they live with an economy like the US has (8 gha per capita)