Vance isn't unique in his obsession with whether people have kids or not. On the Right it's all wrapped up with patriarchal views, fears of "racial contamination", and the desire for the subjugation of women, but even aside from that people are often weirdly concerned with whether or not people have children.
Unearthed video: JD Vance says he and Trump will “go to war against” childless people, who he calls “sad, lonely, and pathetic”: “They should feel like their life is inadequate” pic.twitter.com/dcLZ2wNxyd