Many here (myself at times included) simultaneously admit two contradictory ideas.
a) Before Adam (or any person for that matter) sinned, he was free; and
b) Sin was/is a necessary/inevitable part of creation.
I don’t believe these two statements can both be true. If sin was indeed necessary, it was not within Adam or anyone’s power to prevent its occurrence. Therefore, no one is free to either sin or not sin. And, if indeed it is within the power of a person to either sin or not sin, its occurrence was and is not necessary, but contingent on the free will of humans.
Now, since I think - despite what is often said - most people here really intuitively believe b) over a), I want to address what I find the main difficulty in actually holding that the Christian God created a universe in which sin was a necessary part of its perfection.
The main reason most hold that “we must experience sin” is that it is somehow “needed” for us to experience ultimate happiness and perfection. I think, among other people, Dr. Talbott holds this, as well as Bob Wilson and perhaps many more. “Only in a universe in which creatures learn through experiencing sin can such creatures fully come into glory or perfection” or “only by being educated through the bitter experiences of sin and evil can such beings as ourselves fully appreciate the good” are typical arguments employed.
This notion, however, that sin is “needed” for the perfection of the universe, is I think incompatible with the notion of the Christian God.
A being which has omnipotent power - as the Christian God is claimed to have - cannot be hindered by various means to achieve a certain end (this is assuming man is not really free and that sin was “necessary”). In fact, the more limited ones means to achieve a desired end, the so much less is omnipotence present. I have to eat in order to live. If I was omnipotent, I would not need to do so. In fact, I would not “need” properly speaking anything outside my own will for my own perfect fulfillment. In other words, an all powerful, all perfect God could achieve the good of the perfected universe without employing the means of sin. Whatever reason that can be given for sin’s “necessity” can only get that necessity from the omnipotent will of God. To say at one and the same time that God does not will sin, and yet that he willed its existence as a necessary means by which to achieve his end is to state something logically contradictory. An omnipotent being could achieve his desired result (perfection of the universe) without using evil as a means. If we say he had to use evil means, or that he was bound to, we are admitting that he is not omnipotent, for the use of certain means (as opposed to any means imaginable) to achieve a desired end are evidence against his omnipotence itself. And if we say he actually could have created as much good without the evil but didn’t want to then we’re admitting he delights in evil.
It can again be put another way. Some say we need “bitter medicine” to bring us into perfection. But the fact that the medicine tastes bitter would not be an obstacle to an omnipotent being. He could make it taste sweet. As Lewis said in Problem of Pain: “To say, as was said in the last chapter, that good, for such creatures as we now are, means primarily corrective or remedial good, is an incomplete answer. Not all medicine tastes nasty: or if it did, that is itself one of the unpleasant facts for which we should like to know the reason.”
Such is the problem I see with many responses to the statement that sin was or is a “necessary” part of the creation of an all-perfect, all-powerful, all-loving God. I do not think most here see the actual weight of the problem itself, which is why I’m making a post specifically addressing it. Again, to sum it up, if sin is necessary, it must be because God willed it, but an omnipotent being would not have to have evil as part of his creation to achieve his desired ends; and an all loving God would not want to.
Now, assuming there are some who actually believe with me that a) is true - that is, that rational beings were and are free to sin or not (and any case in which they are not free they cannot be held accountable for “sinning”) - and believe also that sin was and is not necessary… assuming this, I say, I think gets us much further along regarding the problem of evil.
But I will just leave it here for now, and invite those who hold that sin was inevitable/necessary to reflect on the dilemma between its existence and God’s omnipotence/benevolence; and also the seemingly conflicting idea that man is still somehow “free”.
edit In an attempt to make myself more clear, I want to add the following. I think it’s fair to say, logically speaking, evil cannot come from an all-powerful, all-good being. For where would it come from? If such a being is, as the Christian God is claimed to be, perfect goodness, it is quite literally impossible for anything evil to come from him. Metaphysically speaking, good is independent of evil. It (i.e. God) exists “by itself”. In other words, Goodness is self-existent. Evil is what is dependent. Evil needs good; good does not need evil. There can therefore be no necessity in creating a world with evil, for good is self-existent and independent of evil for its existence, God’s will (on determinism) is responsible for the existence of all that is, and God is all good, all perfect, without any darkness in him at all. Again, all this is simply the necessary conclusion of believing the total picture of the Christian God. He cannot do evil, cannot create it, cannot author it; nor does he in any way need it, desire it, or will it. The alternative – supposing he actually doescreate the evil we observe, destroys our notion of evil altogether. But who would say certain things (like the Holocaust) were not evil? Of course, if we admit freedom all this changes. For one, God has lain down his omnipotence, so much of the above may not necessarily be true. And second – which is just as important – it no longer makes sense to say that sin or evil was “necessary”. I do not believe evil adds anything positive to the creation; though God, being omnipotent and omnibenevolent, can “draw forth” good (even goods otherwise impossible) from evil.