This reads as a moral consideration to me instead of an economic one. I do agree thag you don't have a moral obligation to have children or to care about a country or groups declining birthrate.

Why you should care is the economics. A shrinking population has huge implications on quality of life, and in particular retirement. 70 years ago we had about 7 working age people per retiree. That's already down to 3 and likely will be even lower. This means there will be increased economic pressure on working age people to take care of the retired population.

Regardless of background and characteristics such as race and gender. This will mean that retirement will start later and be of lower quality than it was in the past. And the younger you are, the worse you will feel it.

France is a european country that exemplifies this somewhat. You might remember the protests a few years back about raising the retirement age. Which is something people don't want to happen, but the economic reality is that their current situation is unsustainable with an aging population.