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

That's the neat thing, you don't! The very idea of post-tribalism relies on a false narrative. There is an appeal to a mythical past when the Enlightenment was one wonderful big tent and everybody was pursuing the shared project of advancing the knowledge of the human race together. Then those mean and wily post-modernists came and upended the notion of truth. This is all blatantly false. Nobody has ever agreed on anything. As soon as you find a group of people who do agree with you, and there is another group of people who don't, then baby, you've got a tribalism going.

It's a rhetorical move to claim as your heritage some kind of truth that once went unchallenged and is now questioned by people with nefarious purposes. Nothing more.