this seems pretty entitled / clasist in this particular context - many in 'the white-collar upper middle class' are precisely the ones with arguments against having families out of personal preference and those most visibly displaying their preference for other lifestyle choices (after all, if one can afford retirement, one doesn't need a family to support them)
And come to think of it the financial reasons you mention (retirement) is probably one contributing factor from a cultural perspective. If you lack the independent wealth to look after your own interests then you must naturally pool resources with others. If others leave/do their own thing/do better than you that's saying, in a sense, that they don't want to pool resources with you, even if you'd reciprocate. That feeling probably sucks.
On the other hand if you're well off enough on your own, someone going off and doing their own thing/striving for better isn't a rejection or a denial of needed resources. So it can be supported, event celebrated.
Once again, painting with broad strokes. It is possible to point out trends without saying that everyone in a given group subscribes to said trend.
For instance, I'm recently married and the wife and I are looking into starting a family. My co-workers know we want kids, and while about 75% are supportive, there's a couple who have marital/family issues who feed me a daily stream of [insert story about how messed up their marriage/kids are] followed by "so, you sure you still want kids?" in a half-serious tone.
It's a minor annoyance and I just commiserate with the miserable story and laugh it off. But, while I know I'm not supposed to judge as a non-parent there's a few glaringly, blindingly obvious failures of well-intentioned but horribly executed parenting/marriage handling in these stories that set my teeth on edge. Stuff even my parents for all their weaknesses would never have done. When I try to politely nudge back on some of the more egregious points I just get ignored and they keep talking, even when I'm backed up by one of the parents in my team. They seem convinced that they're doing everything the best way it could possibly be done and there's no behavior change on their part that could make it better. On a possibly related note, they're also the team members with the worst health and some of the messiest (if technically functional) code I've ever read. I always wondered where that mentality came from, reading this thread has shed some light on that, given what I know about how they grew up.