While we are a lot of humans, we are nowadays far away from having too much kids.

Worldwide, we are already close to the replacement rate and projections see us falling below by 2070.

Most of the population growth is actually not "new kids getting born", it's "folks getting older than the generations before".

So, if population growth is your concern, don't tell people to have less kids. Tell them to stop getting so old.

Source: https://www.pewresearch.org/fact-tank/2019/06/17/worlds-popu...