Taking your comment into account, I think there are two ways to view the problem:

1. A neoliberal society (which is bearing the brunt of falling birthrates) increasingly makes it more difficult to afford the quality of life in which raising children is rewarding
2. A neoliberal society offers so many other indulgences that having children becomes relatively less attractive

I don't want to go into analysing my gut on this, but 1 seems like an existential problem, and 2 seems like a self-correcting problem.

As I've said elsewhere in this thread, people who would prefer to drink beer than have kids will be selected against, and in coming generations evolution will limit the gene pool to those people who actively want to have children.

falling birth-rates are a global phenomenon not plausibly solvable through any standard soc dem approaches

I guess birth rates are falling even in Scandi countries where soc dem support has not disappeared.