Some people(s) are more easily controlled than others. It's easy to turn some into robots and when the right button is pushed, they will do anything.

This happens in all religions and walks of life. The violent ones are just more obvious and on a larger scale. Education is the only answer and I'm not talkin school. They have to be taught to have more respect for life and the living. They have to be shown that their behavior and beliefs are not for the good of all mankind. And that is not an easy task.