If God is willing to prevent evil, but is not able to
Then He is not omnipotent.
If He is able, but not willing
Then He is malevolent.
If He is both able and willing
Then whence cometh evil?
If He is neither able nor willing
Then why call Him God?
I have read and heard several definitions of "evil", ranging from "absence of God" and "anything that goes against my moral values". Most people, be they theist or atheist, use this word in a literal sense. Most people believe that evil is present in the world, and in some human beings if not all of them. While many people reserve the term "evil" for only the most sadistic of criminals, some refer to each and every one of us as possessing evil.
What is "evil"?
Is it a force, like gravity or inertia? One that we cannot overcome, for it is all around us. Unchangeable. I hope not, for if it is, we are lost. But I do not believe this to be so.
Is it a gene? That notion seems simply laughable.
Is it a metaphor? Like "luck", we attribute it to what we perceive as suitable for the term. "You are in luck!" A word that has little meaning to anyone except the one who uses it in a serious sense. But few people use the word "evil" in a joking manner.
Evil, just like the god who cannot and/or will not free the world of it, does not exist. Referring to something or someone as "evil" does not solve the problem. "He was a suicide bomber." "Aaah. He was evil. It all makes perfect sense now!" This is counterproductive at best. Instead of trying to narrow down the real issue and try to find a way to prevent it in the future, we throw the whole ordeal into a dusty box labelled "EVIL", which not even the strongest minds want to sort through.
Aside from the psychotic and mentally unstable, who are not "evil" for what they cannot help, who is left? I have yet to meet a sane, stable person who did harm to others just for the hell of it. Everyone has justification, acceptable or not, for their actions. There are two types of intentional actions: actions taken based on correct information, and actions taken based on incorrect/incomplete information. Our suicide bomber was told he was ridding evil. He was told that he was doing God's work. He believed this so much that he would end his own life for it. Actions taken based on incorrect/incomplete information.
I am a survivor of long-term child abuse and domestic violence. There are memories I have that sometimes makes me wonder if evil is not indeed present. But then I think as objectively as possible about the mental disorders that these people very probably have, and their own childhood environments. The cycle of violence is not evil. It is something that we can overcome if we realize that we can. Therein lies the problem of evil.
Most people believe that evil is real. They hurt others and breed hate against others because of this incorrect information, perpetuating a cycle of violence and hatred that affects everyone. This concept is perhaps humanity's worst perception. It is this concept, that humans are evil or are capable of evil, that brings out the very nature we classify as evil. It's the ultimate irony. Worse than any religion if you took the doctrine of evil out of them...would it be too much to say that religions would almost be harmless without the doctrine of evil? In fact, would it be too much to say that religions would be long dead without the doctrine of evil?
The problem of evil is that we think it is there.