I’m curious what Friedersdorf and others think about the argument that Christopher Caldwell makes in “Reflections on the Revolution in Europe,” in the course of tackling the question of why Muslim immigrants have assimilated so slowly in much of the European West. Basically, Caldwell suggests that European elites have been so guilt-ridden about their past crimes, and so intent on avoiding anything that even resembled chauvinism or bigotry, that for decades they failed to put any sustained pressure on their steadily-growing immigrant populations to eschew religious extremism or phase out illiberal cultural practices. And worse, their efforts to marginalize what they considered (and still consider) the bigoted attitudes of their countrymen didn’t actually do away with anti-immigration anxieties: They just denied them a place in the political mainstream, which meant that they’ve manifested themselves instead in extreme and counterproductive outbursts (minaret bans, the political careers of Jean-Marie Le Pen and Geert Wilders, etc.).
In my reading and my travels, I've come away with the impression that many European countries conceive of citizenship largely in ethnic terms, or at least that they do so far more than is the case in the United States, where a constitutional view of citizenship based on shared civic values is much more common. This has been true as a matter of law in some European countries, and as a stubborn cultural prejudice in other countries.
It is notable that Europe's integration problem is worst not in first generation immigrants, but in their European born children, and I think one reason they are less successfully assimilated than their counterparts in the United States is the lack of a constitutional creed that successfully inculcates the idea that they're just as French or German or Spanish as anyone else. It's also true that American culture, disseminated largely through media, is many times more powerful than what a tiny country like Denmark can marshal to informally assimilate its immigrant population, and that the heterogeneity of our country means that no single minority group feels isolated in a land that a homogeneous majority dominates. Obviously this is a rough sketch of a diverse continent that inevitably glosses over nuances, but insofar as it holds true, it helps to explain my vexation with Mr. Douthat's reluctance to declare the constitutional understanding of American citizenship superior to the cultural understanding, even if there is some wisdom to be taken from the latter (and there is).