“Is God willing to prevent evil, but not able? Then he is impotent. Is he able, but not willing? Then he is malevolent. Is he both able and willing? Whence then is evil?”
Now, when we take the concepts of "good" and "evil" onto the desk, the debate turns very very complicated.
You have to take into account that good and evil are subjective things created by human mind, and much like moral system (concept of right and wrong), everyone has their individual, unique concept of what is good and what is bad.
Evil as a term is a complex subject to analysis, but it can pretty much be summed up that good and evil are much like light and shadow.
If there is no light, there is no shadow either. It's just dark. But as soon as there is light, there are also shadows - unless the light is in the middle of a n empty room. Then there's just light. Existence of a shadow requires at least two things:
1. Light source
2. Object to cast shadow
If we also want to visualize the shadow, we also need a shade for projecting the shadow o, but tha's not important.
The analogy to good and evil is simple - if there are no differences in people's actions, there is no difference in "good" and "evil" actions. It's all indistinguishable mass of similar behaviour. To create concepts of "good" and "evil", there MUST be a contrast between different behaviour. A very slight difference would be enough.
Consider a small, peaceful village where everyone lives happily in consensus with each other. There are no controversies, as everyone is happy with their lot. Then, one of the villagers notices that his bucket has started to leak. He could get a new one from a shop, but he notices that his neigbour has a good bucket standing on the corner of his yard, so he stealthly goes and replaces the intact bucket with his own, broken one.
Now this is not really a major offensive, but think what it would look like to the hypothetical villagers. No one else has ever "circulated the damage", this is the first time. This villager decided it was an advantage to him to switch the buckets, and what more, he valued the advantage of his neighbour less than his own advantage.
Now this is the most evil thing anyone in the village has ever done, and it creates the necessary contrast to create separate concepts of good and evil.
Similarly, in a village where no one is specifically good and everyone behaves just the same, in a way that accentuates personal well-being. No one can leave their bucket around, 'cause someone would surely take it, and they know it - that's why they don't leave their things around, they lock their doors and they mark their cattle so it can't be as easily stolen. No one cares of each other, but just takes care of themselves in the best way.
In this society there's no real concept of evil and good either. If you steal something, you do, but so does everyone else so it's normal situation. Even if it goes as far as killing someone to get something, you would do it because you know that everyone else would do the same thing. This is alien to us, yes, but so is the number 1 village.
If someone in this "dark" village started to think that "heyyy, wtf are people doing to each other, peace bro", it would be a different behaviour model and it, too would create a contrast between different models, but still it would be up to the people of that village to name the behaviour models. Most likely they would name the old model as "normal" and the new as "strange". Good and evil can, as concepts, only exist in a society that includes both behaviour models.
So, according to this definition of evil (there are others, too), the only way to erase the evil from mankind would be to make all people act according to exact same guidelines, without exceptions. That would practically require destroying free will or perhaps just make the humanity to consist of one individual. Because differences in thinking and actions always create differences (contrasts) between behaviour models, and even the slightest contrast is enough to distinguish light from shadow, or in this case "model one" from "model two", and people can then call model 1 as "good" and model 2 as "evil".
Even God, should he exist, is not free of logical paradoxes.
If evil and good are defined by differences in behaviour models, then evil can't be wiped out if differences are not destroyed. I don't think it would be in interests of anyone to wipe out differences. Perhaps downsizing the contrasts wouldn't be bad thing... but on the other hand, people would still call the "darker" contrast values as evil. Even if there were two "colours" of behaviour models in world, {255 255 255} and {254 254 254}, people would still dub the gray value as "evil".
