I think the argument of selfishness is flawed in the first place. It's based on individuals preferring their comfort, but really on nobody's expense. People suffering discomfort with own parenting then see this choice as an opinion on their own life choices.

Deeper thoughts about economy are not valid in case of your traditionalist acquittances pushing not minding their own business.

I have kids, might have third, economy needs future generations strong and I still think labeling childless people selfish is selfish and arrogant itself.