The birth control pill makes obsolete Marx's concept of the reserve army of the unemployed and is in fact the an effective revolutionary force for social justice, without all the bloodshed and bureaucracy. I think the reason I liked Cohen's book so much is that the evidence, as I interpret it, suggests that people can decide, individually and as societies or cultures, how many children to have, so this route to prosperity really has worked for some countries and can work for others if they so decide. The numbers aren't likely to work. For one thing, population growth rates in poor countries are three times what they were when Europe made its demographic transition and pressure on natural resources greater. Lenin did not wait for Russia to become an advanced capitalist country, poor countries today cannot afford to wait for some unlikely miracle to bring them prosperity before cutting population growth.
Population control is the only economic development program cheap enough to be feasible.
There are no inevitable futures, there are choices, individual and collective. A risk of specialisation that we all face is that we get trapped in our narrow disciplinary perspectives and thus miss important aspects of a broader picture. The most easily controllable variable in the long run is the denominator. Most of the land, land institutions, and land services problems are simpler if there are fewer people. So by the indirect approach of controlling population, a country can dissolve the problems of housing, pollution, political repression, urban sprawl, and poverty that seem so difficult to solve by other means.