I don't know how many times I have started a discussion about God with someone only to hear them say "How can there be a good God when there is so much evil in the world?". I recall the words of atheist Sam Harris who said “Either God can do nothing to stop catastrophes like this, or he doesn't care to, or he doesn't exist. God is either impotent, evil, or imaginary.". I tend to look at the whole question of evil from the other side: "How can there be any good in this world without a good God?".
Just look at how evil people can be. Look at the atrocities they can commit. It seems like each new outbreak of violence pushes the envelope a little further as if evildoers were trying to one up each other! Just try to imagine how evil a person could actually be, what atrocities they could think up to do. I believe it is God who keeps people from being as evil as they could be.
God, in times past, has removed his restraining hand from certain individuals and allowed them to fulfill the evil in their hearts: Pharaoh and Hitler and the like. It's not that God put evil thoughts into their minds or evil desires into their heads, but he allowed them to live out the evil that was already present in them. I can't say that I fully understand why God has allowed these evils to occur, but I know that it is part of an overall plan that, because of my limited capabilities as a finite human, I can't see.
Some people believe that humans are inherently good. They believe that children learn to be bad. I believe the Bible teaches us that we are born evil and only 'learn' how to express the evil that is in us.The Bible teaches that "The human heart is the most deceitful of all things, and desperately wicked. Who really knows how bad it is?". (Jeremiah 17:9).
When something terrible and tragic happens, it's easy to find someone asking how God could have allowed such a bad thing to happen to innocent people. But wonderful things happen to people everyday and I rarely hear anyone asking how God could have allowed such a nice thing to happen to sinful people. It's an act of God when a tornado kills 100 people or a Tsunami kills 3000. But few take the time to thank God and recognize him for his generosity when the sun shines and the sky is blue and the crops grow tall and the children are healthy and happy. No one seems to question where the good comes from, only the evil.