I blame it on mentally unstable people who claim they speak for religion when reality, what they say has literally nothing to do with their religion and contradicts it in multiple ways.

They then rally people together using hate-speech and the promise of power and religious righteousness so they can manipulate people into doing absolutely horrible things.

But if I remember correctly, ISIS's main goal was to establish their own extreme-Muslim nation between Syria and some other country where they can practice super serious Muslim tradition.

Of course, many people in the Middle East are becoming more progressive and are straying from the old tradition where men's roles are pretty much omnipotent and women are just maids and baby-makers.

Because of this, ISIS's only option is to force their tradition on those they "conquer" weather they like it or not.

Anyone who defy them is imprisoned or worse.