This thread is a bit confusing cause people are arguing evil vs threat level and those two aren't that connected. For example, Magneto is a high level threat but he's not evil.
There seem to be two popular sort of villains. The ones who believe in something (Magneto types) vs the ones who don't and therefore are evil (Joker types).
Personally, when it comes to pure evil, I see Shadow King, Selene, Cassandra Nova, William Stryker up in the top. Even Sentinels doesn't seem as evil since they're killing with a purpose and not just for giggles.
Some think Selene doesn't qualify as evil since she has to feed. It ain't her fault she's a vampire! But that's wrong, cause Selene has shown that even if she didn't need to feed, she would. I see Emplate differently. Maybe cause I'm not as familiar with his history but he always seemed more like a junkie to me. Whereas, Selene wanted godhood. Huge diff for me.
Characters like Magneto, Apocalypse, Legion, Mr. M, Proteus may be huge threats but they're not evil (ok Apocalypse is pushing it but still), IMO.
Ehh, to anyone that's not a mutant, Magneto is evil. He is a Mutant Supremacist and believes mutants should rule the planet, and humans should obey them without question (under penalty of death or suffering). This is a constant throughout most of his existence. He's a champion for his people, but in doing so is vile and dangerous to everyone else. Your point about lack of belief being the true sign of evil is a bit weak. Magneto & Apocalypse, for example, have strong beliefs. Both are idealists, but their ideals are dark and ruinous ones for the world at large. The former has held the entire planet hostage to effect political change, for example, and then was on the verge of leading a 16 million mutant strong army against the world to make his ideals reality. Apocalypse is a powerful and ancient schemer, he seemingly respects nothing but power and his ideals lead to a crappy world for both mutants and humans. The former just has it a little better. The lengths he goes to to get his schemes to work is another facet of how evil he is.
I think what you're trying to get at here is that there is a veneer of respectability or higher aspirations to someone like Magneto that soften the evil they commit. It isn't just naked selfish animal slaughter like Sabertooth, or petty desires for divinity from Selene. IMO a ranking of evil would factor in the scope of their evil, the intensity, and the desire of the individual in question to see others suffer and fail. Couple that with the ability, but not desire to be a better person and you get the stomach turners.
In my opinion, any of the evils are so important heroes. I can't perceive evils as bad characters for so much time. I understand their image of a bad guy, but any way I like them.
Arcade is pretty fuckin soulless.