Do post-tribalists even make enough children for them to survive very long? I'm reminder of the Shakers, a religious group that rejected sexual relations between men and women and were famously celibate. They did adopt children at a rate far higher than non-Shakers, but when the supply of children to adopt dried up, their numbers plummeted. Today, there are only 4 or 5 of them left, and when they die, so too will their ideology/religion. Post-tribalism won't survive either, I think.

https://en.wikipedia.org/wiki/Shakers