BRUSSELS — Around the world, this city of great, if often ramshackle, charm has become Exhibit A in the case against immigration, particularly when it involves large numbers of Muslims.

Donald J. Trump called the Belgian capital “a hellhole,” while Lubomir Zaoralek, the foreign minister of the Czech Republic, recently cited the city to explain why his and other Eastern European countries had steadfastly resisted a plan by the European Union to spread Syrian and other Muslim refugees around the Continent under a quota system.

“All the people in the Czech Republic and in other countries see what happened in Molenbeek,” he told a security conference in Slovakia over the weekend, referring to the Brussels borough where many of those involved in the attacks in Paris on Nov. 13 and in Brussels on March 22 grew up.

A closer look at what has happened in Molenbeek and other heavily immigrant parts of Brussels, however, provides a far more nuanced picture than just a generation of badly integrated young Muslim immigrants running amok. In some ways, it debunks the view that Islam is a one-size-fits-all faith that fuels terrorism.