One Trump era argument against immigration that has climbed from the alt-right gutter to respectable conservative circles is that homogeneous societies are
much more "natural" than multi-ethnic diverse ones because people have a natural desire to be with their own. Interestingly, the academic whose work the right invokes to make its case isn't some Nazi nut job but Harvard University's Robert Putnam of the Bowling Alone fame.
Putnam's research purportedly shows that diverse societies have less "social trust" than homogeneous ones because their bonds tend to be looser. But I note in my column at The Week that Putnam has oversold his research and conservatives are overselling Putnam. The fact of the matter is that any the loss of trust due to increasing diversity is a short-term phenomenon. "Over the long run, people reconstitute new identities and bonds based on other shared characteristics. Yesterday's "them" become tomorrow's "us." For example, Putnam notes, in the 1920s, Americans were acutely conscious of divisions among European sub-groups — the Irish, Italians, Germans, Eastern Europeans — and in the 1950s of various Protestant denominations — Methodists, Lutherans, Baptists. None of these distinctions matter anymore."
That's not the only problem with the right's slams against diversity.
Go here to read about the others.