There are many flavors of murdering psychopaths. A few mass murderers from history would’ve been called cliche portrayals today.
The banality of evil is what needs to be learned. Much like fascist rhetoric sounds stupid and is obvious in a vaccuum, when people are drenched in it, A LOT of people slowly succumb to the horrible attitude even if they never start explicitly supporting fascistic positions.
It is poison much like mental illness becomes a poison, slowly enabling mostly normal people to do terrible things, like Todd. Todd was only a psychopath in that he exhibited no sympathy, which a lot of “normal” psychopaths have. It took an enabling environment to turn Todd in to a dengerous captor and murderer.
Dan Carlin called fascism, among other things, an “intellectual contagion.”
Most ideologies and religions are “viral” in the way they spread. Being able to think critically is how one stays immune.
“Enlightened” atheist centrists are often pretty similar to what they claim to be smarter about than people who follow religion and ideology.
And thinking one is “immune” because of their ability to “think critically” is a very solid step to vulnerability. You’ll finde the same wordings for Q-Anon and other conspiracy theorists referring to themselves.