Idiotic.
A rapidly growing population mostly made up of the very young is the demographic model of third world hell holes - while a replacement rate of reproduction is the model of a healthy Western Republic - and a declining population rate is the hallmark of a moribund socialist state.
A declining population rate is hardly a grave threat to humanity, never has been in the history of humanity - we have always been able to generate the necessary population to cover any available food source.
The greatest threat to any human population has always been, and will continue to be, other human populations.
This is typical of most species - the #1 competition they face for resources, territory, mates, or anything else worth having will almost always be from members of their own species.
Please tell us when in the history of humanity a declining population rate has even occurred? Globally, not locally. It has not happened in recorded history.
The Black Plague in Europe? It took a century for mankind to recover economically/socially from that population collapse alone.
You don't know what you're talking about here.