Atheists have for a long time pointed out that evil makes the existence of a perfect God at least less likely, and theists of course have attempted to explain why that is not the case. One interesting aspect of this debate is that, given the way theists argue, there cannot possibly be any amount of evil that would make their God less likely. Their answers to the problem of evil aren’t designed to account for a particular amount of pain and suffering, but for whatever pain and suffering there happens to be.
The free will defense, for example, says that evil is the result of the choices made by fallen human beings (and angels), and that is meant to explain away terrible things no matter how bad they are. The Holocaust, the Black Plague, cancer, atheism — all of these things and more can be blamed on us rather than on the all-powerful being in charge. (The buck has to stop somewhere.) Or consider soul-making theodicies, which argue that what doesn’t kill you makes you stronger (and, come to think of it, that even what does kill you makes you stronger). Or the view that it is simply a mystery why God allows pain and suffering, but that there must be some reason which we puny humans are too dumb to understand. None of these explanations attempts to account only for a certain amount of evil, but rather for any amount we might encounter. No matter what evil may befall us, we should remain confident that there is an all-loving God who has a reason for allowing it.