Judge Claude Frollo longed to purge the world of vice and sin. And he saw corruption everywhere, except within.Clopin Trouillefou on Judge Claude Frollo.
Every day, humans come one step closer to self-destruction. I'm not destroying the world, I'm saving it!Albert Wesker's twisted belief that he is "saving" the world.
Luz: But... why? Why go through all this?
Belos: I'll do anything to save humanity from evil.
Luz: No... You're evil.
Belos: Can't reason with crazy.Emperor Belos conversing with Luz Noceda
Pure Evils who believe that they are never morally in the wrong regardless of their own enormity. As such they mentally convince themselves that their actions are justified, and/or viewing the people who they wronged as having had it all coming, if not also thinking they are genuinely good people. In other words, they do bad because they think they are doing good. Even if their belief is contradicted by reality, they will still believe it till the end. As they always see themselves as noble and/or justified people, no matter how horrible they truly are, their delusions are a major corrupting quality. Ultron, Wallace Breen, Kilgrave, Ego, Shou Tucker, Goku Black, Emperor Belos, Isaac Ray Peram Westcott, Albert Wesker and Light Yagami are prime examples.
NOTE: Villains that only think of themselves as better than others and are self-righteous (e.g. Syndrome, Jill Roberts, Emperor Palpatine, Femto, Lord Voldemort, Lots-o'-Huggin' Bear, Mysterio, Dimitri Rascalov, General Dreykov, Ozai, John Garrett, and Randall Boggs) do not qualify. Those should go under Arrogant and/or Egotists instead. It's mandatory for any delusional Pure Evil villain to think of themselves as actually a good person and keep their mindset even if their actions and motives prove the opposite.
Also, villains who aknowledge their own evilness and take pride in it, but do not exhibit any signs of delusional mindsets, do not qualify (e.g. most versions of Joker, Aku, Contagion, Frieza, Mahito, Freddy Krueger, the Lich, Judge Holden, Mephiles the Dark, Chucky, Ramsay Bolton, and Dio Brando). They can only qualify if they met aforementioned criteria (e.g. Bill Cipher, Roman Bridger, Junko Enoshima, Yuuki Terumi, Longlegs, Sauron, the End, Scarlet King and Norman Osborn).
These villains are the opposite of Misguided Pure Goods.