Agree with all this. I think the lowered birthrate is all explained by the accessibility & acceptability of birth control. Before birth control, if you didn't want to have kids, you had to be celibate, which uh no, thanks. So lots of people had kids whether they wanted them or not. Now that we have a choice, we're finding many people just choose not to.
If this is a problem that we want to solve, then the solution IMO is to treat child rearing as the full-time job that it is. I don't mean subsidies or tax breaks, I'm talking a full $70k/year salary for the job of Being A Parent. As a childless person myself, I would support this.