Such people hijack airliners and crash them into buildings. Such people blow up marketplaces. Such people imprison and torture without due process of law. Such people execute the condemned. Such people start wars. They may be religious, they may be atheists, it hardly matters.
They are found on both sides of any violent political issue, calling for stern retribution and destruction upon those whom they see as the "bad people". They are the mirror image of one another, and they make the World bleed.

Sadly such people do not have horns and could well be living next door to you or I.

But are such people as you describe born like this or are they created. You could argue that if they were created that there would be many social and political factors for this and you would be correct. But is the role of organised religion to help show the way or to confuse it. Often it would seem that organised religions intentionally complicate whole issues and then distance themselves from the results of this confusion.

What is good and bad is a fairly basic concept for individuals faced with a choice of actions. And yes this is simplistic and in my view such things should be encouraged to be seen in simple terms. I am always suspicious of attempts to make such concepts appear more complicated than they are so that we then feel we need 'experts' to advised us.

'Thou shalt not kill' works fine for me as a spiritual basic guide as the how to treat my fellow humans. 'Thou shalt only kill under certain circumstances that we will inform you of nearer the time' does not.