The dark tetrad traits — psychopathy, sadism, narcissism, Machiavellianism — exist on a continuum; everyone scores somewhere on each trait, and this undermines the binary 'monster vs. non-monster' label.
Shaw introduces the dark tetrad and explains that these traits are continuous — everyone scores somewhere on each — so the line between 'evil' and 'good' people is artificial.
transcript
Julia Shaw: each trait on the dark tetrad, as it's called, which is the four traits that are associated with dark personality traits, so things that we often associate with the word evil, like sadism, which is a pleasure in hurting other people, Machiavellianism, which is doing whatever it takes to get ahead, narcissism, which is taking too much pleasure in yourself, and seeing yourself as superior to others. And then there's psychopathy. Psychopathic personality specifically often lacks in empathy. And it's usually characterized by a number of different traits, including a parasitic lifestyle, so mooching off of others, deceptiveness, lying to people, and again, that empathy dimension, where you are more comfortable hurting other people because you don't feel sad when other people feel sad. Now, all of those traits, psychopathy, sadism, Machiavellianism, and narcissism, all of them have a scale. And so you can be low on each of those traits or you can be high on each of those traits. And what the dark tetrad is, it's actually a way of classifying people into those who might be more likely to engage in risky behaviors or harmful behaviors and those who are not. And if you score high on all of them, you're most likely to harm other people. But each of us score somewhere.