The Problem of Evil
God is "Omni-Benevolent" (All good)
-Being all good includes completely opposed to evil
God is "Omni-Potent" (All-powerful)
-Being all powerful includes being able to create a world without evil
Thus, if God is all good and all powerful then the world can't have any evil. But, the world DOES have evil, so God (so-defined) can't exist.
Common claims or defenses to this "Problem" are as follows...
-Evil is necessary for good.
-Evil helps create human morality.
-Evil is God's judgement for sin.
-Evil is the result of human free will.
-Evil makes greater goods possible.
-Ultimately, good outweighs evil. (Or reaches an ultimate balance.)
-Deny the reality of evil.
-Redefine God.
-There can be no response.