Bangladesh, Dec. 27 -- There is an old rule in politics and an older one in propaganda: if you want to weaken an idea, dont argue against it—degrade it. Make it sound coarse. Make it look angry. Make it appear incapable of self-restraint. Over time, people will recoil not because the idea is wrong, but because it has been made unappealing. That is precisely what appears to be happening to Islam today, not only through the work of its external critics, but—far more dangerously—through the conduct of some of its loudest self-appointed defenders.

In recent months in Bangladesh, a troubling pattern has emerged within segments of Generation Z activism and among figures associated, directly or indirectly, with so-called Islam...