The fact that the Islamic State kills other Muslims is often proffered by Barack Obama and others as a sign that it is itself not Muslim. In reality, the fact that the Islamic State kills other Muslims is a sign that it considers itself the arbiter of what is true Islam and what isn’t, and considers itself to have the authority and right to execute Muslims whom it considers to be heretics and apostates. Ansar Bayt al-Maqdis – ISIS-affiliated extremist group in Egypt – has released images purporting to show the execution of a 100-year-old man. The group, who rebranded...