Sometimes poor countries have a lot of people;

India has more than 1 billion residents. Indians are relatively poor, and we know that as families become wealthy, they tend to limit their number of children. So, a much wealthier India, over time, would probably have much fewer than 1 billion inhabitants. Would this make for a better India or a worse India? Although each Indian would have much more, there would be fewer Indians. As a result, is there any argument for keeping India poor, so as to have a higher number of people? If not, why not? In general, what can economics tell us about the ideal number of people in a society? Anything at all?