The division between psychopath & sadist is not as neat & simple as the author makes out. The essence of the psychopath is that he/she experienced unbearable pain so early in life that he/she disconnected from his/her emotions. Thus the adult psychopath feels an extremely limited emotional range—mostly anger vs non-anger. [They feel pleasure, but pleasure is not an emotion.]
The psychopath is typically not content with this extraordinarily limited emotional range. As a result, many if not most seek a wider range through intense vicarious emotional outlets. I.e.: a psychopath may, & usually at routine intervals does, inflict extreme emotional, physical, or some combination thereof, pain on the victim of choice. The victim’s tears, anguish & other displays of authentic emotion express, in at least a limited way, one of the prime emotions the psychopath cannot experience first hand. The true psychopath may elicit other emotions in those closest to him/her as well, in order to vicariously at least witness, since he/she cannot feel, those emotions too.
I.e.: psychopathy can mimic sadism to a disturbing degree. I would trust Krauthammer’s judgment on the ISIS majority more than an untrained diagnosis. Islam is notorious for producing psychopaths. The children witness & experience, at extremely tender ages, precisely the kinds of horror and pain that are most prone to create psychopathy. [Think of the children forced to witness their mother’s death by stoning. There are many other examples as well.]
I think some people are born psychopaths, without conscience and without empathy. This is a challenge to Christian faith.
Some children are born at risk, and their experiences push them over the edge.
People can be trained to be sadists - to dehumanize others and glory in destroying them. And people can be trained to enjoy Roman circuses, or bull-baiting, or any number of sports involving death. People can enjoy hangings and drawing and quartering and lynchings. But these people are not necessarily psychopaths - they can be loving and selfless to those within their circle of loyalty, to family, faith, tribe, comrades at arms.