We have a lot of shortages in this world, but human beings aren't one of them. Any incentive for procreating is, at best, antiquated and, at worst, contributing to the overpopulation of the planet.
That's true in the 21st century, but it wasn't true for most of humanity's history. In addition, there was always a population-level competition between countries (you out-breed the other guys, then conquer them by brute force). I'm not sure whether in the age of jet fighters, strike drones and nukes this competition makes sense anymore.
