This to me is just assuming a blend of Christian baggage like the fall, total depravity, hell and penal substitution. Humans can choose not to sin. We are judged for what we choose to do. An evolutionary trait or urge? In my view Jesus didn’t come to save us on God’s end, he came to save us from ourselves on our end. Notions that he literally took on sin are incomprehensible to me. Sounds like incoherent babble. Nor do I accept that God requires the shedding of a fluid that carries oxygen throughout the body to forgive us (Mitchell calls thisnblood magic). Just genuine repentance.
But I think your post mixes up issues. Because from the start you say: “This question is for those Christians who believe that god created humans using evolution without the dark side to their nature and that the Fall is a description or allegory of a real historical event i.e. humans disobeyed or turned against God in the past; and that this somehow explains why humans have the potential and tendency to commit sin (such as mass murder, war, genocide, infanticide, etc).” But then later you ask how we reconcile the fall (whether real or allegorical). I am not sure who you are aiming this at.
I think many of our proclivities to sin are the product of enculturation. How many children (and adults) are starving to death right now as many of us are living the dream, buying bigger and better. I certainly feel guilty and we are more prone to buy ourselves things than become good Samaritans. Sure, the Michael Shermers could argue we are not programmed for morality at a distance but for those of us who believe in free will this is not a valid excuse.
At any rate, I take it that God knows how to judge us accordingly. A quote from Mere Christianity by Lewis I always found informative.
Human beings judge one another by their external actions. God judges them by their moral choices. When a neurotic who has a pathological horror of cats forces himself to pick up a cat for some good reason, it is quite possible that in God’s eyes he has shown more courage than a healthy man may have shown in winning the V.C. When a man who has been perverted from his youth and taught that cruelty is the right thing does dome tiny little kindness, or refrains from some cruelty he might have committed, and thereby, perhaps, risks being sneered at by his companions, he may, in God’s eyes, be doing more than you and I would do if we gave up life itself for a friend.
It is as well to put this the other way round. Some of us who seem quite nice people may, in fact, have made so little use of a good heredity and good upbringing that we are really worse than those whom we regard as fiends. Can we be quite certain how we should have behaved if we had been saddled with the psychological outfit, and then with the bad upbringing, and then with the power, say, of Himmler? That is why Christians are told not to judge. We see only the results which a man’s choices make out of his raw material. But God does not judge him on the raw material at all, but on what he has done with it. Most of the man’s psychological makeup is probably due to his body: when his body dies all that will fall off him, and the real central man, the thing that chose, that made the best or worst out of this material, will stand naked. All sorts of nice things which we thought our own, but which were really due to a good digestion, will fall off some of us: all sorts of nasty things which were due to complexes or bad health will fall off others. We shall then, for the first time, see every one as he really was. There will be surprises.”
I think the harder question is why were we created with such violent and aggressive tendencies. Is this how God wanted us? What role does this play in omni-benevolence? Why are we like this?
For some the ontological hierarchy of life is a ramp rather than big steps. Chimpanzees in general may face the same issue as we do just to a lesser extent with less moral culpability than we do because we are more evolved and able to make freer choices. Just because something is deemed “natural” in the animal world doesn’t make it so or justify us partaking in the behavior.