Argument from the Infinity of God
As Augustine and Jonathan Edwards pointed out, it is not enough to ask merely what some sin is that requires judgment, but whom it is that sin is against. Shooting your neighbor’s dog does not merit as great of a punishment as shooting your neighbor, because the offense is much greater in the second case. If you have an infinitely good God then you have a great offense against that God. The greatest! (It is no objection to say that the meaning of “infinite” in the context of God’s goodness or nature is unclear, for this is a well-defined concept in more philosophical discussions of theology proper.) The flip side of the goodness of God is of course wrath. Annihilationists do not understand the seriousness and gravity of what it means not just to sin but to sin against God. It is a sin deserving an infinite punishment because of the God it is against.
Argument from Continual Sinning
God commands us to, “Love the Lord your God.” Any deviation from this is sin. Of course, it may not seem to us that we are sinning in violating this command, but that just goes to show our exceeding wickedness. But note something. The sinning doesn’t stop once the sinner is confined to hell. Rather, there is an ongoing revolt and rebellion against God. There is not suddenly a regeneration where the person is loving God and neighbor as he should. Perhaps the unbeliever will exhibit a passionate desire to go escape from hell, but that is it. Wanting to escape punishment for sin has nothing to do with repentance from sin. Since sinning does not stop once an unbeliever is in hell, neither does punishment for sin ever cease.
Questioning the Arguments
Annihilationists have heard the two arguments above before. They have answers to such arguments. Some are good. Some are not. But the two arguments above for an eternal conscious punishment of the wicked and the way that annihilationists have traditionally responded to them bring some interesting questions to mind.
Perhaps the eternality of hell just is the non-existence of the unbeliever. It is even argued that we do not know which is worse punishment for the unbeliever, eternal conscious torment in hell or eternal non-existence. But the reply to this claim follows from identifying just what it is we mean by “worse,” for it is the subject (that is, the individual) in view. Eternal non-existence cannot be a worse punishment for sin than eternal conscious torment, for there is no subjective experience in the eternal non-existence of the subject. And the punishment needs to fit the crime, remember. Any punishment is a worse punishment for the unbeliever than is eternal non-existence, since any punishment that is not eternal non-existence involves conscious subjective experience with respect to the punishment for sin in view.
It would seem that God would not have to continue to punish an unbeliever for continuous sin if God were to just eliminate the sin and the sinner through eternal non-existence. But there is a problem here as well, because every moment M that an unbeliever exists is an M at which an unbeliever sins. Any punishment P for sin requires M (see the paragraph above). That is, if P then M. It is the case that P. Therefore, M. Again, every M involves sin. Thus P will go on forever.
I am shooting from the hip here, so I may have missed my target entirely, but I suspect there must still be something in here worth thinking about.