You can look at ISIS as the enemy, or you can get even more grim about it:
Our species is fatally flawed.
If a brain can get so dogmatic as to want to kill anyone in its path that does not agree with it, then this is a biologically based problem.
Why does the brain need agreement? Or getting larger: Is this really just an example of the pecking order gone insane? What is the mind trying to do here? Why does it need this incredible one-way order? Is it the same drive that makes for slavery?
It is so wonderful that evolution took our minds to a place where we are able to think about so much and to do so much. But like everything, the process didn't necessarily stop at the nice spot.
Things fall apart.