Malthusian catastrophe. Population tends to grow exponentially, but not the resources. Historically, the excess of population have been controlled through wars and famines. The CP wanted to control with laws instead...
The thing is that in developed countries this kind of laws are not necessary because people just don't have children because they are too expensive.
The thing is that in developed countries this kind of laws are not necessary because people just don't have children because they are too expensive.