So the ideal is no one ever dies (most good!) while everyone makes more people (more good!). I guess eventually we'll figure out how to eat rocks. It's not sustainable. Earth is an island that has finite resources. We're covering it in crops to feed humanity, but in the process of doing so are making the planet less hospitable. Should we act now to prevent what we know will happen if we continue pretending like expansion is the only way?
There might be no ideal, but it's very much preferable that everyone has a good run and nobody has to kill their kids or die of pneumonia at 20 or some such.
How much to breed is a separate question, but equilibrium with the environment doesn't have to be at the point of paleolithic misery.
I think I can agree there's a happy middle ground somewhere between "paleolithic misery" and "late stage capitalism climate change induced neolithic misery". Both are extremes of misery of a sort. There's still plenty of suffering now... More if you consider the difference in population between the paleolithic and now.
A global society which works collaboratively to maintain both our modern technosphere _and_ a livable, habitable biosphere. Progress doesn't have to come with all of its current negative externalities -- most of them are driven by short-term profit driven thinking that doesn't take our collective biosphere into account.
