High levels of population growth are unsustainable. There's a finite amount of land and other resources on the planet, and we've seen world population go from a billion in 1800 to about seven billion now. That level of growth cannot continue without triggering wars, famines, etc., and slowing it is a pretty admirable goal.

Infant mortality and subsistence farming in the developing world is one of the big causes for it. Raise the quality of living, prevent babies from dying, and people suddenly don't need to have 20 kids to subsistence farm a plot of desert.

It's only counterintuitive if you don't examine it closely.

You might want to read Jared Diamond's book Collapse, particularly the chapter about how population pressure contributed to genocide in Rwanda.