In chapter 7 of Is There Anything Good About Hell?, I argue briefly that there are degrees of punishment in hell precisely because there are degrees of sin.
Recently, I stumbled across an excellent and concise essay at The Gospel Coalition by Albert Martin and Fred Zaspel that does an excellent job of explaining the rationality of hell’s degrees of punishment. It probably doesn’t warrant an entry into the literature database, but it is worth a bit of your time. Some excerpts are selected below.
It is the fool who reasons, “Well, if I’m going to hell, I might as well have my (sinful) fun in the meantime!” Every day given to sin, every venting of lust, every untruthful word, every next sin committed only adds to the punishment that will be assigned. It would be better for that man to die young than to live only to accumulate a lifetime of sin that will return to him in divine wrath.
This appears to be at least one reason why there must be a day of judgment at the end of time. Final judgment is not fixed upon the death of every individual sinner: it is not until the end of time that the full effect of the influence of any one life can be measured. The omniscient God will take every individual life and assess every aspect of its influence—sometimes an influence that extends for centuries. And on the basis of the accumulated influence of evil, God will mete out punishment upon the wicked.
As wicked and as guilty and as deserving of punishment as Sodom was, the greater sin belonged to Chorazin and Bethsaida, for they had seen and heard our Lord himself and had refused him. And for their abuse of such great light and privilege, their judgment will be the more severe.