Here’s the problem concerning the principle of sufficient reason. If one posits that God has a good and sufficient reason for having allowed the Holocaust, the follow-up question obviously becomes, “Well, what is it?” Any particular answer proves woefully inadequate, ludicrous to contemplate, or even just plain morally abominable. Sometimes it even leads to a reductio ad absurdum. And when this is pointed out, the response simply shifts to something else, which on inspection is equally inadequate or grotesque.
So talking about God’s morally sufficient reason for allowing the Holocaust is akin to speaking to the ontological mystery (the mystery of being) itself. It’s incomprehensible. You can’t reach it. But with regard to the Holocaust, maybe you can’t reach this sufficient reason because it doesn’t actually exist. And if there is no morally sufficient reason for God permitting the Holocaust to happen, and the Holocaust nevertheless happened, then the theistic project itself collapses, for God is supposed to be all good and powerful.
That’s why it’s important to ask, “What was God’s morally sufficient reason for the Holocaust?” If you can’t think of any, what’s left of theism? Silence perhaps, like Thomas Aquinas adopted at the end of his life, or simple fideism? Belief in God after the Holocaust, it appears, requires a leap of faith that deliberately runs contrary to human reason.
Is there really any other theistic alternative? A command theory of God (whatever is, is right, so stop asking questions)? I don’t think so.
So if you’re a theist, where do you go intellectually after the Shoah? After WWII and the Holocaust, Albert Camus thought the first question of philosophy was whether or not to commit suicide. For the religious believer, I think the first question has to be, “What can one believe about God after the Holocaust?”