“Look at how a Catholic or a Jew is treated, and look at how we are treated,” Abdelkarim, a Frenchman of Italian origin in his late 20s who was serving a five-year sentence for armed robbery, told me in 2012. “They have their weekly prayers; in this prison we don’t have Friday prayers. Their rabbi can go to all the cells; our Muslim minister cannot. There’s kosher food, but no halal meat. They despise us, and they call that laïcité.”

In fact, Muslim ministers can visit Muslim inmates in their cells but usually don’t do it for lack of time, and halal meat is increasingly available. But such misperceptions are common, and they only reinforce the appeal of Islam as the religion of choice for the stigmatized and the oppressed. Unlike Christianity, it has an anti-Western and anti-imperialist bend.

One young French inmate of Algerian origin told me in 2013, “If you are a Muslim and ask to participate in the Friday prayers, they take your name down and hand it over to the Renseignements Généraux.” (The Renseignements Généraux is the French equivalent of the FBI.) He added: “If I try to take my prayer carpet to the courtyard, they prohibit it. If I grow a beard, the guards call me Bin Laden, smiling and mocking me. They hate Islam. But Islam can take revenge!”