Capitalism contributes, yes. But, if humanity stays below replacement rate, humanity goes extinct.

Also, no matter how you distribute resources, there are periods of life when your productivity is less that what you need to survive. Everyone has this for many years at the beginning of their life, and those lucky enough to live long enough will have this toward the end of their lives, as aging is the disability that comes for us all. The proven method to sustain persons during those periods is to have enough people in their productive years; it generally requires more than the replacement rate. And, if that doesn’t happen, the less productive suffer and die more.

www.youtube.com/watch?v=Ufmu1WD2TSk

All that said, I’m against encouraging teenage pregnancy, and for full bodily autonomy – no one should be forced to let anyone else use their uterus.

The Earth’s population has nearly doubled in my lifetime. I’m pretty sure we’re not quite endangered yet. I’ll also point out that poor countries that tend to spawn brown players are well above replacement levels if you count those as people.