A machine can be programmed to fulfill its creator's requests only and it will not care about itself, completely selfless and only existing for its master's needs. But humans are not machines. They can't get over their nature because it's their nature - a leopard can't change its spots. We can try to get better, to become more responsible and responsive. But not cast off our humanness. That's how I see it.
I agree with some points of your reasoning. The world is actually OVERPOPULATED, the resources that the earth has is very limited.
The key is to control the population. That is the reason why China has a one-child policy before. The trend nowadays is that a lot of people prefer not to have children because having a child needs a lot of resources, it is a responsibility.
I feel the world can be a better place , if people accept responsibility and if we train our children to take care of the earth. It is a matter of discipline but it is not difficult to do. Taking care of the earth has little to do with having children or not, but more on having discipline. The human race needs to continue.
If human being is so smart, there should have been no problems at all and we all could have lived happily forever. However, as you know, it isn't. But since we have some brain thankfully, we can and have to stop unfortunate things. If we know we are selfish, we should cure it.We must get over our nature.
As for another race that takes our place after the extinction of us, I can't think of anything about them when it's too heavy for us to take care of ourselves.I suppose they'll live well by themselves somehow and it's none of our business. Maybe they can built a perfect peace not like us.
We have to stop to think if it's really good and necessary to bring a kid here as one of mortals. I think we can only choose this way because we have responsibility for kids who doesn't exist yet, unless someone can instantly solve all the problems we have this minute. Even if you need someone to take care, it can't be the reason why you have them.