> I want to attack the premise that a shrinking population is inherently a problem.

It's not really a problem, it survival. Not having kids is not really a problem, but the fact is that you genes will die along with you.

Same for culture. Your own culture dying might not be a problem, but it means that your values will die along with it.

Having equality between individuals is something to strive for (in my western opinion), but does this same value mean that your culture will die out, together with its values? Another culture might survive, because they have less 'favorable' values.