> The US foreign born population peaked in the late 19th century, at 14.7%.
This is flawed because you're not even bothering to count the 2nd generation or generations after. The effect of immigration doesn't go away after the 1st.
> with rising anti-immigrant sentiment emerging for the same reasons, at almost exactly the same percent.
Yes, you've repeated this from another one of your comments. You're still pretending that assimulation doesn't happen.
"Yes, in the 19th century there was a lot of racism and prejudice directed towards the Irish, German, and Italian immigrants. Not surprisingly, they did not destroy US society or culture. Instead, the US absorbed respective parts of their cultures and assimulated all of their populations over decades. now they are an integral part of America"
> fortunately I don't think environmental or other issues are playing a significant role yet, at least not in terms of direct infertility
> It's not existential because it is the most absurdly self-correcting problem imaginable
Unfortunately, there is mounting evidence that the more industrialized a country becomes, the more its populuation becomes infertile. Related studies account for socioeconomic changes i.e. even without socioeconomic changes like the sexual revolution, fertility would still trend down. Air pollutants, endocrine-disrupting chemicals, and heavy metals are linked to reduced sperm motility in men and accelerated ovarian aging in women globally, even in places that are more traditional culturally. The only region untouched now is Central Africa.
> But ultimately it's not even a choice. On top of the cultural issues, I think immigration is simply also unrealistic on a long-term scale.
America has relied on it since its inception. It has only reversed course recently. It's been proven to work for hundreds of years now. Canada has also relied on it since the 1970s since their birthrate was no longer sustainable. They also only reversed course recently.