Furthermore, if the population stays the same but ages, there will be major ramifications to SS.
Furthermore, if the population remains constant but fewer and fewer people have children, then those who do have children bear more and more of the burden of providing for everybody else’s retirement. Responding with “so what, SS will cover me whether I have children or not” is kind of missing the point. And leads straight back to the first point. In a world that requires people to have a substantial number of children to survive (like our world with SS), economically disadvantaging people who prioritize having children is a huge risk.
Nobody is economically disadvantaging people with kids. The question at hand is how much we as a society are choosing to advantage them with tax benefits and social services. Including free education! Having kids is pretty great.
Childless people pay into the system like everyone else. They aren't freeloaders.
As a parent myself I find this kind of savior complex incredibly embarrassing. We have kids, great. I'm glad our government offers tax benefits, services, and an immigration process to encourage population stability. But let's not pretend we're Atlas holding the nation on our shoulders.