(Book: On Guard, by William Lane Craig. Chapter 10: “Is Jesus the Only Way to God?”)
When you’ve dug yourself into a hole that you can’t climb out of, step one is to stop digging. Unfortunately, if you stop digging, people might think you’re admitting that you’ve dug yourself into a hole you can’t get out of. In theological contexts, the way to handle that dilemma is to dig yourself in deeper.
But we can push the argument a notch further. We can show positively that it’s entirely possible that God is all-powerful and all-loving and that many persons never hear the gospel and are lost.
As a good and loving God, God wants as many people as possible to be saved and as few as possible to be lost. His goal, then, is to achieve an optimal balance between these, to create no more of the lost than is necessary to attain a certain number of the saved. But it’s possible that the actual world (which includes the future as well as the present and past) has such a balance. It’s possible that in order to create this many people who will be saved, God also had to create this many people who will be lost… It’s possible that in order to achieve a multitude of saints, God had to accept a multitude of sinners.
What Craig is arguing (without realizing it) is that it’s possible that there is some greater power than God, some power that forces God to do things He would prefer not to do. There’s no logical necessity that requires one or more souls to be damned in order to save someone else’s soul, even given free will. You might think that free will would reduce the chances of everybody being saved, but there’s no logical necessity that says the salvation of one soul requires the damnation of another. (Plus, an all-loving, all-powerful deity would not leave such an important matter to mere chance.) There must be some other power, then, that forces God to do what He would not wish to do. And if there’s some greater power than God, then God by definition is not all-powerful.
And Craig is only starting to dig himself in.