I think this problem threatens democracy and liberalism. If a country like North Korea can maintain twice the fertility as the South, having double the workforce and number of intellectuals is going to allow it to catch up quick.
If SK’s TFR was say 1.22 instead of 0.89 you end up with a 37% larger workforce and only need to convince 1 in 3 women to have an extra child. There’s more enough women who would WANT to have children if it were less of a burden.