Do you have a modern example? Racist Japan or China? Socialist England? Blonde Sweden? 1950s melting pot America was successful, but that was 70 years ago, riding a technology wave from WW II. An AI robot war with China would set up a new technology wave, at least for the survivors.
Not homogenous in race, necessarily, but in culture. And America used to have something called “The Melting Pot”, until the Cultural Marxists decided that was racist, and insisted on it being a “tossed salad”.
I would rather live in racist Japan than outside Philly where I reside.