There's a difference between deciding an ideal population size and enforcing it. Also, there are different ways of enforcing it, many involving little that we w

There's a difference between deciding an ideal population size and enforcing it. Also, there are different ways of enforcing it, many involving little that we would term coercion: establishing child tax credits, for example; funding schools and healthcare via mechanisms which make raising children more or less burdensome. Free people can react to these incentives via their own free choice while society at large, acting as a collective of free people, decide what these incentives should be. The incentives established by other people's choices are inevitable unless you want to go live like the Martian.