LUHE: I actually answered that; my views are similar to Bernhard Haykel. tl;dr: ISIS is in important ways deriving their teachings from the Quran.
While I don't think ISIS is as historically accurate as they portray themselves to be (read the article) I do not (and have not!) at any point denied they derive many of their teachings from the Quran, which I consider to be full of morally outrageous teachings, often using natural interpretations,
Now that I have pointed out I have answered this question can you now explain how we go from that fact to demonstrating that "to be a good Muslim you have to be a butcher and a rapist"? I will make it easier for you: I will be content with a demonstration that a good Muslim have to be a rapist.