The skeptical British, meanwhile, wonder why they should have to fund, and depend on, Europol, the union’s weak security agency — and have to work with countries like Germany, which seem allergic to any sort of surveillance. Better, they feel, to leave the union, retake control over their own security, and rely instead on the world’s most powerful intelligence alliance, the American-led “Five Eyes.”

And so the detonations continue. Should the British vote in June to leave the union — the so-called Brexit — other nations, such as Hungary and Poland, will be tempted to follow. The European Union could dissipate faster than even its detractors could have dreamed.

So are Germany’s critics right? Is it reasonable to pull up the drawbridge?

In a way, the very question shows the disproportionality of the thought — unless you think it’s worth sacrificing 60 years of peace and international cooperation to the depredations of terrorists. It’s what they want; European disunity, confusion and extremism put them a step closer to the all-out war between Muslims and non-Muslims they so desperately seek.

And yet the opposite of anger, apathy and self-delusion, is also the wrong answer. For the sake of social peace, after the Sept. 11 attacks, and later after the Madrid and London bombings, we told ourselves that Islam and Islamism had nothing to do with each other. But sadly, they do. The peaceful religion can sometimes serve as a slope into a militant anti-Western ideology, especially when this ideology offers a strong sense of belonging amid the mental discomfort of our postmodern societies.

Brussels in particular is a city of bubbles, with parallel communities untouched by any sense of national identity. When I was a correspondent there, the sharp difference between the prosperous city center and its depressed western and northern fringes, where a majority of the city’s poor immigrants live, represented the worst kind of ghettoization. And it mirrored Belgium’s national split, between Dutch-speaking Flemish and French-speaking Walloons, making it difficult to direct allegiance anywhere. As a Walloon socialist told King Albert I in 1912: “Il n’y a pas des Belges” — There are no Belgians.