Well if a father wants to have unassailable parental rights over his children, he still ought to be married. If he's okay being beholden to the mother's whims, then there's no need for marriage.

The better question is since when can you have kids without being married? Until quite recently you were ostracized if you had kids out of wedlock and illegitimate children had fewer rights.

The answer to your question is: Since a few million years. Nevertheless, I understand your point.

My point was more along the lines of criticizing 'correlation vs. cause' and providing equally weak arguments.

What I believe is that there are multiple factors at work here. So higher home prices are probably one reason why people are deciding against children, but most certainly not the only one. And 'deciding against children' doesn't mean they will never have any children, maybe they just wait a few more years before they get the first and in the end there will be one less for some couples.