There is an obvious difficulty for anyone who believes both of these things. For suppose that we divide everyone in the world into two groups: A, those who are saved, and B, those who are damned. If God knows ahead of time who is going to saved and who isn't, it seems he could have created a world with only the members of A in it. So what could possibly justify his creation of those destined for hell?
When challenged with this problem, Christian philosopher William Lane Craig answered that perhaps it isn't possible for God to create a world with only people who are saved. For let's say God created a world with only those in group A. In the actual world, all of these people are saved; but it doesn't follow that they would all be saved in this other world that contains only them – for in that other world, things would be different, and we cannot say that in their different circumstances these individuals would still freely come to accept God.
This is obviously a rather weak defense of the Christian view. However, for the sake of argument, let's say Craig is right and that at least some of the people in group A need those in group B to be around in order to be saved, so that God had to create group B.
This is where Schieber's argument comes in.
The argument employs the concept of philosophical zombies – hypothetical beings that look and act just like normal humans but that have no conscious states. Such beings aren't plausible, of course, but the point is that God could have created them. And though such beings would have no conscious experiences of any kind, to us they would be indistinguishable from real persons. Your best friend could be a zombie and you'd never know.
But now, even if it is necessary for the individuals in group B to be around to interact with those in group A, it's obvious that everyone who is a member of B could have been a zombie rather than an actual person. This way, they would still provide those in A with the same exact circumstances that allows the latter to be saved, but – the crucial point – they wouldn't be damned, for they wouldn't even be real persons with a soul. So it seems hell cannot be justified.
Pearce points out that, as a way out, a Christian could conclude that this half-zombie world is what God in fact created. Since from the outside one cannot tell a human from a zombie, conscious humans like you might be surrounded by zombies who merely appear to be conscious nonbelievers. (This puts a whole new spin on the claim, made by some, that there are no real atheists.) But who can seriously entertain the idea that some of the individuals around us are zombies?
Moreover, such a Christian would be abandoning the concept of hell as a real place – references to it, as well as the zombies who act human, would all be part of a grand deception on the part of God. And that suggests another way for the Christian to reply to this zombie argument: God would never create such a world because it would involve deception on his part. (On the other hand, would such deception really be worse than consigning some of his creatures to eternal suffering?)
There is one thing I disagree with Pearce about. He claims that, even though a Christian could consistently believe that we inhabit a half-zombie world, he himself knows that we don't, since he is a nonbeliever and yet knows that he is not a zombie. I'll leave it to the reader to think about that one. As I said, lots of food for thought in this book.
Pearce's book on Amazon