Yousef Bartho Assidiq was on the path toward terrorism, part of a group whose members discussed beheadings and mass attacks. Now he tries to stop other youths from getting radicalized in his native Norway. Assidiq’s story of conversion to Islam and recruitment into a militant group is not uncommon. His rehabilitation is the kind of accomplishment that participants at the Global Youth Summit Against Violent Extremism next week seek to replicate. The Sept. 28 gathering at the United Nations comes a day before President Barack Obama hosts an event on countering extremism in New York.