I absolutely agree with you OP.
I don't want to get hung up on labels. Around 1% of the population is thought to have some sort of sociopathy/psychopathy/anti-social personality disorder. All sociopaths are narcissists (although not always vice versa). Whether it is due to genetics or major trauma in chlidhood or whatever, they are quite different to the rest of the population. Their brains are literally wired differently.
They have no conscience
They have no empathy.
They like to control and dominate.
They are, however, emotionally intelligent in the sense of being able to read others' emotions in order to manipulate them as necessary.
Their lack of conscience is actually quite a major thing to get your head around if you are a 'normal' person with a conscience. But it's crucial.
Unlike 'ordinary' people, brain imaging shows that when these people are shown happy faces they feel negtive emotions. When they are shown sad or fearful face they feel positive emotions. This is why they act nasty. Causing others suffering, even in very subtle little ways, makes them happy. Here stands your class bully, your sabotaging colleague, your abusive partner.
They can't form truly meaningful, loving relationships and so they get very bored and can only really get their kicks from high thrill activities (many have addictions) and manipulating others. Life to them is a game in which they relieve their boredom or generate their twisted kind of pleasure by manipulating the people around them and watching the results. When you ask "why on earth would they do that", when they do something mean, this is the answer.
This is why it is so important to better educate ourselves about the existence of this 1% of humans who hide in plain sight.
If we don't realise they exist, we misattribute our own emotions and motivations to them. This is very dangerous because they do not share them and so we make mistakes dealing with them.
We tend to give them second chances or the benefit of the doubt when we shouldn't.
We spend too long trying to fix them when we can't.
We spend too long trying to figure them out when it's simple: they lack a conscience, lack empathy, and are only nice to you (they can be very, very nice!) when it will get them what they want.
We try to get even with them when we can't. They love your anger as well as your unhappiness because it shows they have an effect on you.
If we saw them for what they are we would do the only thing possible: walk away and engage as little as humanly possible. Thus they lose their power. Also we would warn other people, and they don't like being rumbled because it spoils their game.
I could write more.