When you think about the conditions that make choice meaningful, the need for atonement and the inevitably of damnation both pop out.

Meaningful choices require meaningful consequences. Something must *happen* because of my choice. As Bruce Charlton points out, real choice means that the chooser must become a miniature first cause from which a chain of effects prepends (I’m not sure I’m using “prepends” correctly, but the word popped into my head, and my policy is always to use words that pop into my head—I’m not going to look it up—that would be unsporting). So whether or not we are created beings and whatever our ontological nature may be, if free agency exists we are to that extent necessarily ontologically punching in God’s weight class. (As an aside, this means that either God must exist or else we must be eternal, or else we live in a material determinist universe and all love and thought and happiness is an illusion. I leave the exact argument as an exercise to the reader (as an aside, this may be the first time I’ve used the ‘I leave the exact argument’ construction where I actually have worked out the argument in my head). And since love and thought and happiness can’t be an illusion, because in a material determinist universe there is nothing to be illuded . . . )

So far, so good. We exist, we make choices, the choices have consequences. Unfortunately, by punching in God’s ontological weight class, we are punching way out of our league. Which is why the choice to make meaningful choices—the Fall—is not called the Triumphant Ascent. Probably all of our choices have bad consequences that we are not able to fix and many of them have primarily bad consequences. These bad consequences are unjust. Set aside for now whether it would be just for us to make choices of eternal consequence on the basis of necessarily partial information. Instead, think about the bad consequences our choices inflict on other people. They do so in all sorts of ways. They have to, by definition, or else we wouldn’t be able to interact. An interaction that doesn’t have the possibility of meaningful effects, that doesn’t convey information or change anything, is not an interaction. But bad consequences inflicted by someone else are unjust. God is just—He wants to fix those bad consequences, or at least compensate for them. But the more fully the consequences are fixed—the more fully they are compensated for—the less meaningful the original choice becomes. Imagine how differently we’d feel about murder if the dead came back to live, rested and happy, after 24 hours. Imagine how differently we’d feel if they came back to life rested and happy in a second. Imagine if they came back to life instantly, and God wiped everyone’s bad memories and shock instantly away. Isn’t it obvious that under such conditions the murderer’s choice, and the non-murderer’s choice, don’t mean much.

Therefore, there the consequences must not be erased, only transferred to another (SPOILER: Jesus Christ). That way we can be relieved of the consequences without being relieved of the ability to make meaningful choices.
But the choices are still only meaningful to us if we care about the person they are transferred to. Consider the sinner who chooses not to repent. If he cares about Christ, then he suffers knowing that he caused Christ to suffer for no reason. If he doesn’t care, then no matter what blessings and compensations the Almighty heaps on him, no matter the paradise he is given to live in, he is still someone who has lost most of his ability to make meaningful choices and be an agent. It follows that damnation is not a supererogatory act. It is inherent in meaningful choice. The soul that rejects repentance must either eternally suffer the pain he caused and is causing Christ (if he cares about Christ); or else, if he does not care about Christ, he must accept the futility of his own choices and live as something other than a purposive agent; or else he must be allowed to suffer forever the consequences of his own sin. Each of those three alternatives is damnation.