Altruistic evil” is a striking term coined by Jonathan Sacks, the former Chief Rabbi, now a global campaigner for religious understanding, in a challenging new book, Not in God’s Name, published this week. He uses it to describe the appeal for young, Western-born Muslims of fighting alongside Islamic State (IS) in Syria and Iraq. Before their radicalisation, Sacks notes, many of those now on the battlefields were regarded by family, friends and fellow students as friendly, tolerant, moderate people. So how can they have become so devoid of conscience as to participate in the so-called Islamic State’s chilling acts of barbarity that have been condemned as contrary to the Qur’an by leading Islamic jurists and theologians? His answer is “altruistic evil”.