This is quite literally mathematically irrefutable, no matter how many levels of obfuscation one piles on. A society with a fertility ratio of 3 will eventually

This is quite literally mathematically irrefutable, no matter how many levels of obfuscation one piles on. A society with a fertility ratio of 3 will eventually supplant one with fertility ratio of 1, it's only a matter of time. Much like climate change, however, this takes generations upon generations, so people like to pretend it's not the case, and shift the burden to their grand-grand-children. But mathematics does not care about one's beliefs - it exists irrespective of them. A societal group with sub-replacement fertility is dying out by definition. You can easily put together a spreadsheet, put in the death and birth rates and model this hundreds of years into the future. In fact you should probably consider doing so - it's rather eye opening.