he knows it's wrong but he's overcome with so much grief, suffering and hatred that he just doesn't care anymore or he wants vengeance on the rest of the world.
Depends on the character.
ONE type of "evil character" could be so as you described.
But this is not the only type.
Just believe, for example, someone who is a racist. He believes it is "good" to perform a genocide. It's what he (or she) believes in, there is no "he knows it's wrong", because there simply is no "wrong" in his or her belief-system.
Fanatics act the same.
There are other types of "evil characters", I suppose, which differ only in som,e points - minor points rto our eyes, maybe, but possibly fundamental in this character's layout.
Though that's an interesting definition, I don't think all fanatics behave like that.
One example: Factors like "absolute obedience" and "total filial piety" might over-ride his sense of right and wrong. The trick is to not think about it, to sweep the issues under the carpet and pretend everything is fine. In Asia, we've got this saying: "you don't see it, you don't hear it, you don't speak about it"(the blind, deaf and mute monkeys).
The person may know that "all these acts" are absolutely wrong on many levels and might even criticise them but might also have been ingrained to pretend the act is right or to even ignore it.
That is: if the person did think about it and did consider such issues, then his "perfect world" might fall apart. He "knows" it is wrong but yet his brain registers it as "doesn't know": a paradox.
Or: As long as _____(father/mother/relative, etc.) declares that I must obey, I will obey even if the decision is morally wrong and even if millions of lives will be affected.
Of course, there're many other ways to define a fanatic and so-called "evil characters".
And besides, just 'cos a person talks about genocide, doesn't mean he'll do it. He might be some sort of fanatic but how much harm he causes will depend on who he comes in contact with and whether he actually is placed in a situation where he'll have the power to inflict harm or to influence others.
Oh yes: in certain Asian societies, there's this practise of assimilating various qualities from various cultures or countries. Now by itself, it isn't so bad as other cultures do it too. However, many usually blindly adopt these "values/qualities" which will often result in a 180 degrees change in moral values, principles, point of views, etc. Now consider this: a pro-peace society which practises this has been heavily influenced by a pro-war country responsible for various war crimes like rape, genocide, etc. What do you think might happen?
