[rayiner]

> If you bring in a bunch of immigrants it'll still have recognised centres to the distributions. That is literally how the US population was built.

Yes, but the center of the distributions along various axes will shift. To give an example: I grew up in Northern VA, which in the 1990s was quite WASPy. One aspect of that culture was austerity: it was hard to tell the people worth tens of millions apart from upper middle class doctors and lawyers. Now, the influx of immigrants from Asia and the Middle East has totally destroyed that norm. Relatively discrete brick mansions are being turn down and replaced with enormous and ostentatious displays of wealth.

> Indeed, if we assume that migrants migrate to places with cultures that promote success then change the culture that'd suggest that migrants cause mean-reversion for the worse.

That’s the concern. And it’s not just “success.” But orderliness, egalitarianism, democracy, etc. Most societies are much less successful on all those fronts than America. The only direction we can really go is down.