In the short-term, immigration and ethnic diversity challenge community cohesion. Extensive multivariate analysis of a large national sample of Americans has found that (with many other factors held constant) people of all ethnic backgrounds tend to “hunker down” and become less trusting of all races and ethnicities (including people of their own race) in more diverse neighborhoods.. The Financial Times reported this with the headline "Harvard study paints bleak picture of ethnic diversity." There were some reactions, pointing out that the article only focused on Putnam's second point (his first was that diversity is beneficial, the second was the one that's above, and the third was that society can overcome the challenges), as well as pointing out the article wasn't racist.
Lastly, there was a piece pointing out that the article was realistic, and that it's important for society to realize the challenges it faces. I like this last piece's conclusion:
As David Goodhart, the editor of Prospect magazine, has long argued (to initial abuse), to indulge in liberal fantasies about the purity of victimhood is to betray both host communities and immigrant ones, for it assigns to the former the charge of at least incipient racism and to the latter the eternal status of privileged victim - a position which, to be sure, can be both profitable and eagerly sought, by those who know how to play victim politics.
I'm probably as guilty of this as anyone else, throwing up a rallying cry for "victims," and it's definitely something to keep in mind . . .