...
And what does fertility rate have to do with anything?
It's well known that people from area's with high infant mortality have more children than people with higher survival rate.
And that poor people have higher average number of children.
...
All of the data from the opening post is from populations living in the United States.
Fertility is a major component of
Biological Fitness. If you judge your biological fitness to be unimportant then the fertility data can be ignored as tangential. Others may feel differently so I included it.
But artificial manipulation of fertility through contraception or other practices would make it only useful if you managed to discount those practices.
Just because an intelligent couple choose to have no children has no necessary meaning to their true "biological fitness"?