I didn't downvote but I find the thinking superficial to the point of crudeness.

I often joke that the Amish are the "meek" who will "inherit the Earth".

also didn't downvote, but clearly there are confounding variables (fertility also correlates with poverty, for example)

There is a common argument that X social group has a lot of children, thus they'll become a greater proportion of the population over time (typically applied to developing countries, immigrants etc). These arguments are flawed because humans don't really work this way, and adopt k vs r selection depending on environment.

I don’t think the parent claimed that beliefs are genetic or even that they are 100% heritable; only that conservative, religious populations have higher fertility rates and consequently the next generation will disproportionately come from a conservative, religious background. Many liberal atheists also come from conservative religious backgrounds, for example. This much at least doesn’t seem very controversial to me.