for population problems. Any policy has its limitation and side effects no matter how perfect it looks like.
Overpopulation leads to rapid consumption of any kind of resources and speeds up the destruction of ecosystem. It induces unhealthy internal competition (jobs and living space) and affects quality of daily life (pollution or convenience) within an ethnic group. How to slow down the growth of human population has been an urgent issue worldwide.
Your one child policy concern is also valid. Let us hope that the leaders know exactly which policy is appropriate for the time being