First off, I am willing to "define" God as He who shows himself through, and in, the world, and who is good (which is as much a definition as defining you as He who shows himself through that body is a definition of you, but it is kind of helpful). I begin with the premise that God is good. I'm not going to argue for it. Perhaps another time. Now, the world is, itself, corrupted. God is not corrupted. The world is. It's the same as the fact that you aren't sick in your person just because your body is (though there are plenty of cases where your body's sickness makes your person sick in some way, such as being cranky from lack of sleep, but that is because we are embodied in that way, whereas God is, while in a sense embodied, not in that way). The world's corruption is there to show us who God is, though. God is he who shows himself through and in the world, and the world, here, means everything. God shows himself through the world in that whatever occurs in the world only occurs due to his will. He shows himself in the world--he stands in the world--in those places where he is revealed to us.
Did God cause the Holocaust? God does not show himself in the Holocaust, but he does show up in the Holocaust. He made himself appear to people--not necessarily visible, but as surely as if he had--through the events surrounding and including the Holocaust. Here is a counter question: those people who became Christians because of the Holocaust, not because of the horrors of it, really, but because it brought them into contact with people who truly believed and who showed it--who revealed Christ likeness by their way of life--and who were blessed to share the Good News that Christ has dealt with all the evil of the world, even conquering death, were they saved by God, or humans? If humans, then it may be that humans caused the Holocaust. If saved by God, then God saved them in whole, and the Holocaust, as part of that whole, must be considered caused by God. But! This causing is not the sort where one can point at God and say "you killed so many Jews!" Rather, one can only say, "God, all that pain, for human souls? I don't see how it was worth it." And he responds "not yet--look at the Cross where my Son bore all that evil--it is finished." Some will say that the loss of faith for many outweighs the gain of faith for a few, but how can anyone who truly believes ever turn all the way away from Christ? If they fell away, then they never really got it to begin with.
Does God condemn some to hell, and save others? Well, in the end his actions are all for good. Is anyone's dying and going to hell good on its own? I doubt it, and I don't think God sees it as good either. Yet it happens. On the other hand, anyone being saved is good all on its own. This means they must be distinguished: God does not cause the former in anywhere near the direct way he causes the latter. God shows up in salvation, but not in damnation. Damnation is where we start, he doesn't need to intervene. Even in those places where it appears that God keeps people from seeing him--where he hardens people's hearts, or blinds them, or speaks in parables so that they do not hear and understand--he is not resisting their seeking of him. Those who seek Christ's life will be found in it, while those who seek their own life will find it... to be death. People don't seek God unless he impels them to. They may seek something like God, but it is their own idea of God.
Here: the good reveals God, the bad reveals our need of God, and the redeeming of the bad reveals Christ. And in the end it will all be made good: the bad will be redeemed. God will be glorified above all.
So, I think I believe in single-predestination in the only way that makes sense to me, but I'm not so sure there is a difference between this form of single-predestination and double-predestination where God is yet without fault.