Q: If there's a God who is good and all-powerful, why does He let horrendous evil in the world?
A: Because His good is so transcendent that it makes up for it.
Therefore it is reasonable to be optimistic.
I just ran across this extraordinary argument I've never heard quite put that way. I have intuited that God's good triumphs over evil even to the extent that I don't need the promise of an afterlife to follow. I took it as an article of faith at a very early age without a great deal of what I would consider religious instruction. I might even be willing to suggest that it is human nature to expect so, except that the actual atheism and religious instruction are pervasive. Still, Marilyn McCord Adams makes a compelling case. You see, if you don't believe in God, the horrendous evil problem is not the faithful's, but the non-believer's.
Now in one way, this is precisely what Hitchens decries. If you can be forgiven, if your communion with God gives you comfort, then to a certain degree you can turn irresponsibly away from the grotesque evils of the world. You might even, in extreme cases, be convinced that you can get away with perpetrating such deeds. And certainly people rationalize away those great crimes as God's will. But then to be Christopher Hitchens is to be a man of no optimism, or one quite deep into whiskey. Why? Because logically, if you don't believe in a transcendent good, then there is no reason to be optimistic if you are a victim or a perpetrator of a horror.
Now let's define horrendous evil. We're not talking about dropping your ice cream at the circus. We're talking about dropping a cluster bomb on the circus. Evil with a capital E is the sort of occurrence that you walk away from, if you can, with very deep questions about your ability to move on in life. And what's crucial to understand is that life-wrecking evil is happening all of the time. It's not just a capital H Holocaust once every century, but the great capital crimes and crimes against humanity which pollute human life on a daily basis. We know this evil continually exists in the world otherwise the initial question could be exceptionally qualified.
Adams cuts to the chase on the 'free will' answer as well. Free will as a gift is not self-justifying unless a transcendently good God who is not aloof gives it. Her example is that if a Kindergarten teacher left razor blades around the classroom, 'free will' is a lousy excuse. Such a neglectful person could never heal the wounds caused by the exercise of free will. But God, or at least the Christian God, does rehabilitate through an abiding faith in His grace. People come back from beyond the brink of despair. Jesus saves.
I don't think anyone has such faith in psychiatry.
So is the atheist who believes only in a materialist universe kidding himself? Logically, if he is optimistic, he is kidding himself. Or perhaps by force of personality, he can just decide to be eternally optimistic in the fate of mankind no matter what. My understanding is that Kant would call that an illusion. So whose illusion is better? Call it a toss up?