They are savages. They make the nazis look good by comparison.
Indeed. But it has to be asked: were they spies who were killed? Spies within ISIS should know they might be getting in over their heads. (terrible pun....the onslaught of bad news has gotten to me)
The Nazis and the COmmunists in Russia and China and in Cambodia and Cuba all used this method, The Terror. It is not so much to punish unbelievers as it is to cow the population.