Atheists claim God doesn't exist, and one of the arguments they use for this is that there is evil in the world. If God exists, they claim, He must be evil because evil exists. However, by claiming God doesn't exist, they must acknowledge that evil cannot be God's fault. Something that exists only in fiction can have no effect on the real world.
In acknowledging the existence of evil while rejecting the existence of God, atheists reject their own argument. If evil exists, and you currently acknowledge that it is not God's fault, it is illogical to say that God's existence suddenly makes it His fault.
An atheist might object and say "then how can good be from God either?" Of course, Christians have a different starting point. An atheist can claim good comes from man too, but the reason a Christian can reason that good can be credited to God whereas evil cannot be blamed on Him is that evil is ultimately that which is opposed to Him. Life is a good thing, and can be credited to God because He is the one who created it. Murder is an evil thing because God is the final authority over who gets life. Whoever takes a life unjustly is usurping God's authority, and is fully to blame for that particular evil. Even when God deals out capital punishment, that is still a response to evil, meaning it is 100% the sinner's fault.
Therefore, any atheist who argues that if God exists, He must be evil, is arguing inconsistently. Only a Christian can have a consistent view of the morality of God.