> Ultimate purpose of any biological entity is to survive and reproduce.
Yes, but not to infinitely grow. Any animal population with unchecked growth will eventually be culled by their own outgrown presence if their environment cannot support them. Humans have deemed current society cannot support their children in the ways they deem important.
Thus we've culled ourselves, not by over-grazing, but by using our own reasoning.
In this case, Humans are capable of supporting as large or small population as we'd like. The planet would support it. What the greater challenge is, is resource allocation. We've collectively decided society-by-combat is the most efficient way to allocate resources and because of that, some people have checked out and used what power they have to not continue that game.
The people deciding not to have children will be the same that suffer in their old age. That is their vote.
This is a fundamental issue with current economic system which borrows from future generations to keep going, often with dire consequences as we are seeing these days. Infinite growth is literally the core concept of modern economics. We need drastic changes to our economic models if we need to change any of these. But even then, you need above replacement rate to sustain a stable society which is unlikely to happen with current narratives around gender and social matters.