This Republic is perhaps unique (OK, maybe Canada - maybe) in its demonstrated ability to assimilate immigrants from all over the globe. The "Melting Pot" has taken Irish, and Italian, and Polish, and Chinese, and all sorts of folks, and produced a hard but supple alloy called "American".
Some say that this process continues to this day. I'm not sure, because some new immigrants don't seem to want to become American.
Certainly there's an incentive structure in place, where professional race-baiters like La Raza get power and influence from immigrants not assimilating.
This strikes me an a unique experiment in our history, one that explicitly turns its back on the success factors that we've seen over the centuries. "Reckless" is one term for that. Progressives are pleased to roll out the "Precautionary Principle" to justify their policy preferences regarding energy policy, saying that a sufficiently bad outcome - no matter how unlikely - is a powerful justification to stop something.
OK, I'll play that card here. Maybe race-baiting multiculturalism is unlikely to cause widespread rioting and death. Still, that would be such a horrific outcome that the Precautionary Principle says we have to STOP. RIGHT. NOW.
Right, Progressives? I mean, your argument is entirely persuasive.