>>7
That would be the "problem of evil," which has been debated for millenia by nearly every religion, except Buddhism and the dualists.

Some popular counterarguments:

• Evil doesn't actually exist, it's just the absence of good.
• Since good and evil exist, that means that a moral law exists. Someone created that moral law, and that someone could have only been God.
• God must have a benevolent reason for allowing evil to exist, but it is beyond our comprehension.
• Evil exists in order that we have free will, which necessarily includes the freedom to do evil.

I personally think the free will counterargument is the most convincing.