" Muslims can say that slavery is not legitimate now, and that crucifixion is wrong at this historical juncture. Many say precisely this. But they cannot condemn slavery or crucifixion outright without contradicting the Koran and the example of the Prophet. 'The only principled ground that the Islamic State’s opponents could take is to say that certain core texts and traditional teachings of Islam are no longer valid,' Bernard Haykel says. That really would be an act of apostasy. "

― Graeme Wood