People don’t not want kids. Lots of people want kids at the right time. Others want it but find they would be unable to provide for their children due to a generation and a half of wage stagnation, along with women not wanting to have to change their profession to “full time childcare”.
Giving people access to childcare is documented to work. There isn’t some magic cultural collapse. It’s just capitalism squeezing everything out of people, and people worn out from it.
I'm not sure which Gen Z's you've spoken to recently, but the next generations certainly want kids much less than previous generations. And this trend will only continue. We have seen family sizes continually drop, until now the average is about 2. That will soon drop below 1 where most people do not have children. Give it 30-40 years max.
If you only care about population decline, you have an easy to undrestand tool for solving this problem, that doesn't involve trying to establish cultural hedgemony to try and convince everyone that they have to have at least 2 kids each.
People have been predicting the imminent demise of civilization from lowering birth rates for an awful long time.
Actually I think people acts according to circumstances. Kids are a blessing and a burden at the same time, always have been, and some other factors helps decide.
But unwanted pregnancy is not "a help to decide" and it's weird to say that the fate of civilization should rest in people being unable to have safe sex.
Low birth rates are only seen as a problem in the context of race or nation: "if we don't reproduce, our genes/our culture will disappear and foreigners will replace us". Globally there's no problem at all. When low birth rates extend to the whole planet, the problem will solve itself very quickly by elemental incentives.