The impact of extremely low birthrates is not only economic but cultural.
After two generations of close to 1.0 children per woman, here's the result:
* Every child has no first cousins.
* Every child has no aunts or uncles.
* Every grandparent has only one grandchild.
Think for a moment of the impact of this. Big family gatherings at Christmas would be a thing of the past. Elderly people would have virtually no grandchildren to spoil or purchase gifts for. It would be a lifeless culture, to say the least, without small children, tiny voices, and bustling schools.
Incidentally, this is close to happening in Italy, Portugal, and Greece. The birthrates are close to 1.2 after about forty years. And do you think citizens of these countries will be spawning babies after their governments finally collapse due to excessive social spending?
Yes, a sure sign of decline, decay, and ultimately fall, when grandparents are outnumbering grandchildren. This has been going on in Europe for decades. Native European populations soon to be outnumbered by non-European immigrant groups, primarily muslim.