The extreme mode of 50% of child-bearing age adults going 0 kids is not necessary and will probably end up being disastrous.
What happened to the Shakers?
But I think looking at this in global terms is wrong-headed anyway, whether you're for or against. The question is whether a specific person should be a parent here and now in specific personal circumstances. So of course it tends to be selfish. It's not entirely selfish since others are involved locally, including the future child. But "the world needs more children" or "the world needs fewer children" is barely relevant at all.
It's a choice I made for myself, that I am ready to bear the consequences of, say paying a greater share for other's childcare/making society more family-friendly/later retirement. I just would not want to add another ~copy of my soul to this pile. Yet I respect those who do.