Earlier quoted context omitted.
So what? If people think that their children's future will be worse than their own, it doesn't really matter what people experienced 500 years ago. A common sentiment among parents is giving their children more opportunities and a better life than they had. If some people don't feel like they can do that (regardless of whether it's true or not), I imagine that's a powerful demotivator around having kids.
Yeah, so if you are familiar with human history and the exponential curve of increasing human wellbeing that we're riding and you still feel strongly that the future will be worse, then the conclusion should be that you're probably in an irrationally negative emotional headspace for some reason, not that you're right! (I say that without judgement, having been in that exact headspace myself not too long ago.)
In the lead up to the 2008 financial disaster all the bulls were saying "the housing market only goes up" without any understanding of the underlying shifts that would come to bear. It's easy to predict the status quo, they didn't need any thought, they could be replaced with a rock with "housing goes up" written on it.
For the first time in decades, risk of global conflict is rapidly rising. Two revanchist empires in the east are eager to reclaim lost territories and see their chance as the American hegemony that presided over the long peace faces stagnation & decline. This is the stuff that makes world wars. Who wants their child to live through that?
But fine, anyone can write "human well-being only goes up" on a rock.