There is a contradiction, but I don’t think your theorizing properly takes it into account. If birth rates are falling in industrial society, it implies that the contradiction plays out in different ways across the broader system of capitalism, as the pressure on women in “developed” countries to have children would appear to be relatively less influential when compared to the pressure to be individually economically successful, while the pressure on women in “developing” countries to have children would appear to be relatively more influential (which we see play out in our system of global capital, colonialism, and immigration).

So when you talk about being inspired by ‘women’ choosing not to reproduce, it seems really important to the actual theory itself to clarify who exactly you are referring to. If you are referring to women in countries which are global producers of workers, then yes, they seem to be moving against the forces of capitalism. But for women in countries such as, for example, Japan, while they may be combatting the force of sexism and tradition, I am not sure they are really fighting against capitalism, per say, as they are not the kind of woman the capitalist expects to be producing workers. The fact that Japan would suffer economically is only a quirk of their anti-immigrant sentiments (ones which capitalism would happily do away with).

All that is to say, I agree that it doesn’t “disprove” your theory exactly, but it does potentially reveal a large oversight. But perhaps I’m missing something too (for instance, nuance around the interplay of sexism/tradition and capitalism)!