However, birth rates across the developed world are below replacement rate, so it would be accurate to say that patriarchy & capitalism have become a fetter on the continued development of humanity

I think this is actually one of the contradictions between capitalism and patriarchy - the need to redeploy women's labour in capitalism has weakened the impact of patriarchal control to have more children, particularly when the number of births and pregnancy required is so much less than in pre-industrial agricultural economics.

The replacement rate is the number of births required to maintain a birth rate that existed when patriarchy was wholly ascendant and women had no reproductive autonomy.

While it's quite expensive and difficult for single women and couples that can't birth children themselves, I think the falling rate has a lot to do with women not wanting to have kids or as many kids.

Surely there's more than a few hundred posters here that agree with puberty choice.

An alternative (bad) vision for the future is massive increases in surrogacy, exporting reproductive imperialism to developing and often non-White countries (with a premium on "white" poor women as exists today in Ukraine, at least before 2022).