In the almost 30 years that I have lived in the West, discussion surrounding Islamism has been stymied by one thing: the naïve belief that it will magically disappear. After every Islamist attack, promises are made. Ambitious changes to anti-terror programmes are ordered. Politicians line up to announce that this is the last time. And yet somehow -- despite all the vigils, all the pledges, all the policy announcements -- Islamism remains as potent as ever.