This whole fertility thing is so weird

The fertility thing comes across as so weird because its an actual problem that Republicans don't want to solve in any reasonable way because that will involve threatening their donor's bottom lines. Basically across all developed nations with easy access to birth control, education and modern mechanisms birth rates are falling and in many countries these rates are already well below replacement rate (2.1 children per couple, not percent like RFK Jr said)

The United States was consistently staying above replacement rate via immigration but I have a nasty feeling that isn't the case anymore

The reason replacement rate is so important is Capitalism really depends on growth companies gaining new customers. The stock market in particular relies on new wallets to spend money, homebuilders rely on new people to build homes for, and offices rely on new employees to hire. When populations start stagnating or worse shrinking, Capitalism really starts to fall apart as that causes an ongoing recession as fewer wallets in an economy means less money flowing through an economy. Less money moving through an economy means a smaller GDP which means the the economy ultimately shrinks. Bad economic conditions also lead to people feeling less certain about bringing a new baby into the world so the cycle tends to accelerate before the actual population decline can accelerate noticeably

The obvious solution is to decouple necessities of life from capitalism and significant state investment into improving existing infrastructure and planning for degrowth so that a long term recession and the effects of declining/re-balancing populations do not negatively impact the masses living through them. This is of course antithetical to capitalist and conservative goals, so as they realize this looming threat is upon them they're getting extremely weird about it and trying to find ways to get more families to have lots of babies to try to reverse the trend.

In short, these republican pundits are trying to have a serious conversation about what could be an extinction-level event for capitalism without cluing in the masses to the flaws of capitalism or the fact that its an entirely man-made crisis that doesn't actually involve any scarcity of the necessities of life