This is true at the global level, and especially in the 3rd world, but not in the developed societies most of us are living in.
The Flynn effect reversed sometime in the mid 80s. The pattern is currently for less educated people and people in worse financial situations to have more children than those more well off.
That's significantly concerning given we have extensive evidence genes matter more than environment does in humans:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4270739/
It is far more efficient in the long run for that trend to invert, and the average intelligence of the population plays a huge role in facing the challenges of the future successfully.
Pretending this is not a significant and increasingly dire problem does nothing but avoid confrontation with hard truths.