[nine_k]

The economy can only get bigger with mote people if there is enough food, shelter, and jobs for those people.

China, especially when it was anti-capitalist in 1970s, had trouble with food, shelter, and gainful employment. They had to curb the population growth, or face famine and riots down the line.

After China has in fact embraced private property and market economy, the situation has improved drastically, food self-sufficiency has been achieved, economy kept growing like mad, etc.

After enough people have completed the transition from poor countryside, where you make mote children to have helping hands, to urban settings, the birth rates have naturally plummeted. So they were able to repeal the one-child policy.