ie a replacement rate of 1 isn't some immediate existential threat, and that making arguments like 'species aren't happy' is completely specious ( sic ).
If you want a wider argument - then the reality is the birth rate is dropping because when women have the choice ( via birth control and increased socio-economic independence ) they are largely choosing to have less children. So by definition, given it's a choice - women are happier.
The second bit is speculation on motive - which is why I didn't bother the first time - but in my view, those that push an argument that there is a fertility/species crisis ( using specious arguments like the above ) - who say women aren't really happy with their choice etc - is all about subjugating women to baby making machines to satisfy the ego of people like Musk. Whether the original poster has that motivation or has just fallen for the "species crisis" ( or even worse 'race' crisis ) rubbish - I have no idea - I didn't want to assume the worse.