Sally is in moderate pain and opts for a painless medical intervention that extends her life by one more day just because she wants to experience another day. Surely Sally is not being irrational. It's not irrational to choose to experience another day, even if that day involves moderate pain. Further, whatever the merits of a defense of euthanasia in the case of severe pain (in the end, I will reject euthanasia even in those cases), defending euthanasia in the case of moderate pain is implausible.
This suggests that it can be worth living for a finite amount of time in moderate pain. Moreover, it can be worth doing so even if there is no prospect of pain-free life afterwards. The rationality of Sally's decision doesn't depend on her beliefs about the afterlife. All this suggests a strong intuition that the experience of life, by itself, is enough to make life worth living despite moderate pain. But if it makes life worth living for a finite amount of time, why not an infinite?
Well, maybe an infinite life of moderate pain would result in extreme mental pain of hopelessness and ennui. But notice that this is a contingent consequence. A person who doesn't think much about the future can avoid the pain of hopelessness, and a person who doesn't remember having had many such days can avoid the pain of ennui. Thus it is logically possible to have a worthwhile infinitely long life of moderate pain without any great compensating goods besides the good of experiencing life itself, at least as long as one wasn't very thoughtful.
Thus, it is logically possible to have a painful but mildly worthwhile eternity in hell. It could be a life where enough of people's memories are wiped to prevent excruciating ennui, and where the people's minds have degenerated to a point where they don't care much about the future. (Would it be surprising if the minds of the damned weren't in tip-top shape?)
Now, one of the main reasons people reject the doctrine of hell is because they think that a loving and just God would not allow a person to exist for eternity in a state worse than nonexistence. But if it is possible to have a painful but mildly worthwhile eternity in hell, so that we need not suppose that eternity in hell is worse than nonexistence, this particular argument against hell disappears.
Objection: The biblical picture of hell involves not merely moderate but excruciating pain.
Response: Let's grant a literal picture of eternal burning. Now, being burned is normally an excruciating pain. Either divine goodness would rule out eternal excruciating pain or it wouldn't. If it wouldn't, the objection to hell disappears. But if divine goodness would rule out eternal excruciating pain, then it follows logically that if there is a God and eternal burning, then God does not allow that eternal burning to be eternally excruciating. Perhaps he provides fairly effective painkillers.