Philosopher Stephen Maitzen has an excellent piece, called Perfection, Evil, and Morality, which will appear in a forthcoming volume edited by James P. Sterba. It details some of the reasons atheists find incompatible the existence of a perfect god with the suffering all too evident in the world around us. In particular it highlights how obligated such a perfect being would be to prevent the suffering we see. I recommend it.
One response he has seen suggests that morality has a significance in and of itself. But as he points out it's not something that needs to exist or is worth saving, because it only exists because suffering exists. No suffering, no morality. There is no morality required in a universe populated by senseless rocks.
At the end Maitzen mentions something else that is worth highlighting; the notion that atheists complaining about the problem of evil are somehow "angry at God"; Maitzen writes:
Living in a society still dominated by an inherited theistic outlook, atheists like me are not infrequently accused of being “angry at God” and venting our anger in the form of arguments such as those I’ve offered here. The accusation is patronizing, question-begging, and false. Any atheist who can think straight knows that anger at God makes no sense. I’m no more “angry at God” than I’m angry at Santa Claus for failing to relieve me of the burden of Christmas shopping. If I’m angry at anyone, it’s at those of my fellow human beings who (to extend the metaphor) would say morally outrageous things in order to defend the Santa Claus story as true and to excuse Santa Claus for repeatedly failing to do what the story makes it clear he ought to do.That summarises well how absurd that particular accusation comes off to me, and I think he is right to blame some of this on an 'inherited theistic outlook'. It still puzzles me that theists don't see how abhorrent their attitude to suffering is. For just one example, consider the discussion thread here. A theist called CodyGirl824 (I presume not a Poe) says, in response to an atheist discussing the problem of evil:
The fact that only humans are capable of evil, because evil requires formulation of intent and acting on that intent. So every evil act is an act of free will. Without free will, there can be no evil. If God were to choose to "prevent" every evil act of any and every human being, He would take away all free will, since God can't just intervene when an evil act is about to occur without obliterating that evil-doer's free will, and the consequences thereof. Without free will, there can be no love. Love is God's purpose in creation. (The Bible tells us so). So we people of faith understand perfectly why there is evil in the world as it exists. As we learn from the metaphorical, allegorical, mytho-poetic narrative of Adam and Eve, all acts of evil are acts of disobedience of God. We really do have all of the atheists' and naturalists objections covered. They simply refuse to recognize this fact....and continues in much the same vein despite her many errors being pointed out repeatedly. A sterling job done by her responders on that thread.
Now, to be fair, we cannot judge all theists on one rather obtuse example, but the appearance of callousness in this response does seem to recur in many a theist's response to the problem. What I find callous is the acceptance of suffering in their accounts, when we are taught, and perhaps know, that we should ameliorate it. They are explaining why suffering is necessary, when we (surely) know that it's not.
At least, a suffering-free world appears to be logically possible, and it is surely what is anticipated in heaven, or what existed before this vale of tears was supposedly created. One would expect our world to reflect its maker, if its maker were perfect, and it's simply not. This doesn't strike me as a particularly difficult notion to grasp, and repeated attempts at theodicy suggest that many theists do grasp it.
In the end something must give; their god's perfection, or the wrongness of suffering. Too many refuse to give up their god's perfection.