"Bad seed." I recently saw the term "unmotivated malignancy" somewhere, and it made me naturally think of cancer. Cancers are unmotivated malignancies.
As a Christian and as a Psychiatrist, I accept that there is a dose of evil in every human being. The 7 Deadly Sins are not a joke and there is a universal need for mercy. However, I have paid attention to people long enough to learn that there are certain people who are strongly destructively-motivated because they were "born that way." In casual conversation, "toxic" people who can be well-disguised. You could term it a "talent" like a musical talent which demands expression. Scorpions have a talent.
I am not talking about sociopaths necessarily, or other diagnoses like "Borderline." Just people who were made with a heavy dose of venom in the soul. It requires no medical diagnosis because it's on a normal spectrum, a normal distribution. Perhaps a spiritual diagnosis. Some people also seem blessed with gifts of unbounded grace, gratitude, love, warmth, and forgiveness in their souls, and thank God for that end of the spectrum.
Interesting to me is not how powerfully malevolent people make others suffer but how skilled such people can be at rationalizing their malevolence and destructiveness. "My mother was...." "My Dad was an...." "I got a raw deal..." "People didn't like me". "I was too good/enviable/bad/rebellious..." "I was abused or bullied by...." And so on. As CS Lewis dramatically illustrated, the devil is subtle and more clever and manipulative than most of us can imagine. It is up to all of us to stand up and defeat those things in ourselves, and to steer clear of them in others.
Contra lots of today's psychology, I have come to believe that some people are born with unusual doses of destructiveness and malevolence, of scheming and manipulativeness, and who take gratification in it. Not criminal murdering sociopaths. It is "unmotivated," if you accept that many or most rationalizations are baloney and simple efforts to maintain some "self-esteem." In other words, often the "cause" comes after the pattern of behavior.
Without wanting to get too evangelical on our readers, the devil comes disguised as a friend, a victim, or in the dress of an angel. I am a skeptic about exorcism but I do believe that salvation through Christ can save, reshape, souls. This is not a common view amongst my profession. I am not a "psycho-utopian" (Trademark, Maggie's Farm) in the sense that we would all be wonderful saints if only for this-or-that misfortune, mishap, etc. That is a crazy fantasy.
Evil thoughts are normal for humans. Just thoughts are the limit because we can't help our thoughts. We are all fallen, but to varying degrees. Just my opinion.