I'm all for equal cost for a couple who choose to have a child.
At the same time you can't mandate it. And there's no denying that statistically women choose family more, when choice is given to them.
I know several couples where the wife is essentially asking to retire (in their thirties), to be home with the children and video games, and that the man should continue working for them. Even if it jeopardizes their shared FIRE plans.
If they do that, who is actually paying the tax? Financially the wife for sure. Life quality the husband for sure.
As for replacement, the population age pyramid is not sustainable. It relies not on stability, but growth. The greying of population is inevitable (compared to the classic pyramid) thanks to medical advances and the fact that exponential growth has to stop, mathematically. We can choose starvation, war, plague, or reduced births.