The KKK are Christian. They aren't exactly representative of modern Christianity (or of Christianity back when the KKK was more substantial), although there was a big subset of the South who were sympathetic to them. The comparison is actually very apt. IS or Daesh or whatever you want to call them (I'd prefer Daesh as it is what the locals call them when they aren't pointing guns at them), is Islamic. It isn't representative of modern Islam, or even of Islam in the region. Thier theology is also a pretty piss poor interpretation of the source text of Islam, an argument you would be right to make, just like the KKK bastardised the Bible (note, I don't like the Quran and think it has some horrid ideas but it is pretty fucking clear that many of Daesh actions are reprehensible). But you cant ignore the fact that they appear to be sincere a fair chunk of the time when they say part of their motivation is religious.