I don't think there will ever be a point where the tech you're describing is suddenly available and the world is also just as overpopulated as it is today. I t

I don't think there will ever be a point where the tech you're describing is suddenly available and the world is also just as overpopulated as it is today. I think our approach to the end state you describe will be much more gradual. Our holy books still recommend that we be fruitful and multiply. We still have systems in place (like social security) that will fall apart unless we can maintain unbounded growth. Our society is riddled will all of these leftovers from a time when having more people actually was a good idea. Those memes aren't serving us anymore, and evolution will prune them with time. It probably won't be a comfortable time. Cultural attitudes towards population aside, the nightmare scenario you describe is unfolding in tiny little pockets all around us. There's no need to nuke the poor people all at once when you can just let them starve one at a time. Nobody needs to make the single big hugely unethical decision of genocide, they just need to repeatedly make the small mildly unethical decision of apathy. I'm hoping that we can make the former into a stronger effect than the latter, but I'm not optimistic.