Why the Problem of Evil is really very simple
Technical discussions of the Problem of Evil usually get into issues such as first-order goods and evils, second-order goods and evil, and so on. To the simple formulation that an omnibenevolent being would not allow evil to exist, it is widely acknowledged that the following is a valid response :
(1) There is a morally justifying reason for God to permit evil it could prevent, insofar as that evil is necessary for some higher good.
(all non-ontological theodicies take this form)
More succinctly :
(2) There is no gratuitous evil.
Which is to say :
(3) There is no first-order evil that does not cause a second-order good.
And then the atheologian and the theologian argue on whether (3) is actually true or not, and whatever reason there might be for this or that evil to exist.
Well, there is plenty of reason to think that (3) is false. And the evidential argument from evil, based on gratuitous evils, is a powerful one. We see easily and intuitively that a human being who commits gratuitous evil is immoral.
But the fact is, "God" is not a human being. So there is an inherent problem with posing the PoE as revolving around (3). The relation between first-order evils (say, the suffering caused by a visit to the dentist) and second-order goods (say, better teeth) is a relation of CAUSALITY. The first caused the second, according to natural law.
But if we assume that God exists, then there is no natural law, only divine fiat. Therefore (3) automatically fails in the case of theism. The whole notion of what a gratuitous evil is, is based on the assumption of naturalism. But that obviously cannot obtain if we assume that God exists ! Therefore we cannot portray the PoE as revolving around (3), since God is morally responsible for causality just as much as it is for evil events.
All non-ontological theodicies also fall to the same problem, in that they assume naturalism and its causes hold. The free will theodicy assumes that the nature of the human will is a given. But to God it cannot be a given ! That's ridiculous !
The Problem of Evil is not a Problem of Unjustifiable Evils. It doesn't matter if we can justify the evils or not. We are not the moral agent under question here : we are not God. Our naturalism-based evaluation of the evils has no bearing on the PoE.
The existence of evil alone is sufficient for PoE. The fact that the Christian can evaluate something as evil alone is sufficient to destroy theism. This is in fact similar to the Moral Argument from Evil, which argues from the Christian recognition of evil and desire to change events that Christians do not really believe in God. But the PoE is a statement of fact, and does not proceed from people's beliefs or lack thereof.
My own variant of the PoE, which I describe on this page, puts the focus back on the act of Creation instead of the evil event in a naturalistic perspective. The moral responsibility of God is firmly located at that act. And by pulling back the perspective, we see easily that everything in the universe, not just specific events, are available to God, and that attempts to analyze events from a naturalistic, human perspective is fallacious.
Another error that even prominent theologians fall into, is to characterize the PoE as a Problem of Not Enough Good. They think that we're whining because we don't get the ice cream we want. No, a frustrated desire is not "evil". Only actions are good or evil. It is not "evil" for people to have unfulfilled desires. To try to compare the PoE, which is supported by universally reviled events such as earthquakes and tsunamis, the Holocaust, deadly viruses, or the suffering of a child, to not getting ice cream or not being President, is disingenuous and downright slanderous.