Does the presence of evil discount the existence of a good and omnipotent God? No! Actually, the presence of evil proves the existence of God! Here’s how the argument goes (I thank W.L. Craig for this):
1. Evil Exist
2. Evil (and objective moral truths/laws) cannot exist without an objective basis for evil – God!
3. God must exist!
The fact that evil exist is self-evident. However, premise #2 requires a little explanation. Without an immutable, universal, all-wise, and good God, objective evil cannot exist. If there is nothing greater than the human being, then there is nothing greater than their millions of differing moral opinion, and there is nothing to make my opinion any more correct than yours. Consequently, there is no objective standard by which we can say genocide and sex slavery is wrong.
Also, if morality doesn’t have an immutable source, then it changes and cannot be taken seriously. If you tell me that rape is wrong, I can simply respond, “Maybe not next year!”
If the source is not universal, then we encounter other absurdities. If murder is wrong here but not in Hawaii, I can go to Hawaii if I want to murder. In any event, a moral law that is not universal is laughable.
Also, if the moral law is not given by a good and all-wise God, then there is little reason to follow it apart from rewards and punishments – something that can only breed cynicism. Consequently, God must exist if evil and objective moral law exist.