In my world, there rules a wise government that maintains an Utopia that was created centuries ago. This Utopia was founded by elders that left earth because they felt Earth decayed through wars, famine and - first and foremost - overpopulation.
Hence those elders and their successors introduced policies in their distant Utopia to prevent all the root causes for earths deterioration.
To me, it is however unclear how to keep overpopulation at bay. The goal of the government is to keep the number of inhabitants equal in the long run but which ratio of newborns is needed for not exceeding the population cap taking natural cases of death into account?