If your life is awesome, you don't want/need a bunch of kids to feel important and you've got better things to do with your life than just pump out kids.
My life is awesome because I have kids. It's not an either/or sort of thing. They give me levels of joy that I never imagined before they were in my life. I wouldn't trade them for anything.
Increasing the standard of living decreases population growth, especially when women get a piece of that action.
But I do agree with you there. Lower standards of living are often accompanied by lower life expectancy and higher infant/child mortality rates. More kids makes up for that, and provides more workers to help the family get more food, water, etc.
Increased education tends to lead to improved standard of living, leading to more sustainable and healthier populations. But we don't get rid of the children.