This is Now.
America used to know how to assimilate immigrants
What he leaves out is how easy it is today (and how hard it was then) to enter the country.
And the fact that the trip was, essentially, one way. Then, it was 2 weeks or more travel to get to the US (and roughly the same home) and cost about half a years wages. One left friends and family behind forever, for the most part. One had to commit to living in the "new World" for the rest of your life....
Today you can fly "home" anywhere in the world in less than 12 hours (maybe a bit more if you live in Australia) and easily return, at less than a months wages for most people.
And while thre may have been Irish Ghettos and "Little Italy" and places where only the Polacks or the Hunkies lived, they worked alongside other American.....and had to learn at least some english to communicate and survive....A common language that helped make them all one people. No one accommodated them, they accommodated their new world and new home.
The kids were mixed in together in school and learned English and by the second or third generation were truly amalgamated Americans, even if they held to the cultures of the old home country.
Accommodating our recent immigrants has prevented them from assimilating.