In this last respect, Silicon Valley and Anonymous could do the most good. Weakening and even destroying the web presence of the Islamic State could limit its spread, or at least impede it. But such efforts alone cannot destroy ISIS, since the Islamic State’s Internet presence is only incidental to its broader appeal.

ISIS has not only become the archetypal “strong horse” that, in Osama bin Laden’s reckoning, people will always prefer to a weak one. It also offers an empowering sense of purpose to its recruits, one to which the modern West has trouble responding, as New York Times columnist Ross Douthat argues…