Hi guys! Something I have recently noticed is that some users argue that being Pure Evil doesn't reflect how well-written a villain is and that purely evil villains are often flat characters, like the Saturday morning cartoon villains, who are evil for the sake of it and enjoy being evil. After some examination, maybe that's true. However, as a screenwriter-in-training, I sometimes struggle to write villains and I realized something that many of you may be interested in knowing, but take into account that this is my opinion. You all may differ from what I think.
Some Pure Evil villains can be well-written, but in the following cases:
If such villain is delusional and does think himself/herself/themselves to actually by the hero of their own stories: Villains who don't see any wrong in their actions are interesting to write as they get to be more complex, like Judge Claude Frollo, for example. Since I was a little kid, I always found strange that Frollo considered himself a good guy when the movie showed me that Frollo wasn't one of the good guys. Another example could be Grant Walker, who sees himself to be the saviour of humanity when he wants to plunge the Earth into a new Ice Age. A particular villain example of this (though not PE) is the MCU's Thanos, whose complexity was one of my favorite aspects. He left me with the impression that maybe he actually was a hero after all... Another (this time PE) example could be Light Yagami, who despite his fall into villainy, did some good by erasing most evil from society.
If such villain is insane and does whatever he/she/they wants: Crazy villains who have no sense of morality may seem boring, but some of them, like the Joker or the Green Goblin, can be challenging to the hero, as they are guys with whom the hero can't reasonate. Yeah, they may be too cliché, but inserting one sometimes may create more drama. Especially if you reveal the reason for which they are so evil, giving them a different point of view of life, like in Victor Zsasz's case.
If such villain is a plot devices: If a villain serves a plot device to the story, then maybe he/she/they can't redeem themselves nor have good qualities due to serving the story as the ones who oppose the hero. For example, Emperor Palpatine mostly serves as a plot device to be the reason Darth Vader is so evil and why Vader ultimately redeem himself by turning against his Sith Master. Palpatine can't be redeemable because then there would be no evil from which to pull Vader out.
If such villain is an alternate personality: It may be a bit unrealistic (I don't actually know too much about the Dissociative Identity Disorder), but having a character with an evil personality who behaves like a separate character can be quite interesting because it embodies the negative qualities of the protagonist. Yeah, they may be psychos but could also be complex.
To summarize it, PE villains be well-written as long they don't have few character traits or unclear motives: they must have at least an excuse that could be understood in different ways (for example, I always felt Lotso to be tragic until I realized his possible selfishness). There are even some villains in this wiki that we aren't totally sure to be purely evil, such as Kevin Khatchadourian (who may actually feel remorse for what he did), General Modula (who is speculated to have been brainwashed) or Armando Salazar (who may have cared for his mother and tried to avenge her). If the PE villain is a foil to the protagonist, that makes them even better.
My reasoning when writing a story is that if you want a Pure Evil villain whom the audience is supposed to hate or like, give him/her/them a backstory so the audience can understand why they behave like that. As in real life, I don't think anyone is ever born evil, so many PE villains may have had some kind of event happening in their lives that made them the monsters they are in their stories.