In the case of ISIS? Not so sure about that. You'd be hard-pressed to find a single ISIS member who does not identify as a muslim.
The reasoning for that is quite simple. They consider themselves to have the only true beliefs, and all who disagree with them are heretics who need to either be forcefully converted ASAP or killed on sight. Not the first time, not the last time.
If that's the case, what is the basis or origin of the belief that ISIS spreads with such extremism if not the religion that is Islam?
Any religion can be twisted like this. Remember the Crusades and the Inquisition? They also hindered all logic and progress, though Catholicism has progressed a lot since then, especially in the last few decades (the Crusades are taught to be historical mistakes of Christianity among Catholics, just sayin'). Also, the main motives for the Crusades weren't pious, but more political, which may also be happening with ISIS
If it's never tied to a religion, what then is the belief that they are taking to these extremes?
Tying to a religion is the easiest way of attracting massive numbers of people, especially from rural parts and un(der)educated people in general (though education is no guarantee extremist ideas won't come to one's mind).
ISIS' leaders may not even believe their drivel, they might just be using it as recruitment methods and target marking.
Their interpretation of Islam, radical/political/terrorist as it may be, is taken straight from the Qu'ran. (...) they rape and sell children as bounty exactly like the Qu'ran allows.
Give me some sources (that aren't from sites run by atheists who hypocritically hate everyone and everything who isn't with them)...
Don't know much about the Qu'ran itself myself, but as an example, I once again take Catholicism, which de facto doesn't take Leviticus (from the Old Testament) as a thing (I cringe every time anyone quotes it). It's surpassed by the New Testament's teachings. Hence, as you said, interpretation is key. The right interpretation leads to right beliefs (and right beliefs are those that aren't destructive).
No, that doesn't mean all muslims are terrorists
Glad you agree.
Edited by Plokite_Wolf, 24 November 2015 - 10:18 PM.