And that taboo is probably rooted in evolutionary psychology, people have a genetically driven tendency to criticize those who advocate having less children? So could there be an instinctual drive behind it?
https://www.flashpack.com/solo/relationships/dont-want-kids-...
1) Limiting number of children in rich countries. This is what your links talk about I think. Yes, perhaps there is a taboo in place here.
Is that relevant to sustainability crisis though? Population is already declining in rich countries, quite naturally.
2) Limiting number of children in poorer countries. Well, as in the article pointed to in a sibling comment, "Richest 1% account for more carbon emissions than poorest 66%"...
So by saying that overpopulation is the root of the crisis -- are you not saying that it may be better that 10 poor people are not born, than for rich people to do minor changes to their lifestyle?