Then why did you call them out on being "incredibly un-Islamic" when you yourself acknowledge that the founder of the religion "probably did" keep slaves?He probably did, but that doesn't excuse these actions.
Don't underestimate the power of Divine command theory.i dont know much about islam but i wouldnt bother looking at the books to figure out why people do certain things. the holy books are basically rorschach paintings and people see what they want to so they can do what they want to.
isis/is/isil leaders saw a rorscach painting in a really twisted and fucked up way, and described the painting as such to others.