I don't think you're quite getting my point about human nature. To be clear, I do not believe in predestination and my explanation was an attempt to illustrate why. What I'm saying is that if God made men and predetermined what they were going to be and do, then God really can't punish men for sin because they were unable to not sin. Under predestination man only does what God programmed him to do so how can that be morally wrong? If I made a chair, but wanted a ladder, I would now punish the chair for not being a ladder. That may be a bad analogy but to me, it only makes sense if man had actually possessed the potential to not sin and of their own free will decided to anyway.
I don't really have an issue with why God permitted Adam and Eve to fall because I believe in free will. I can't understand how you can hold that Adam and Eve had an actual choice, but God predestined what choice they would make. That seems incoherent to me. Rather, in my view, God did actually give Adam and Eve free will to chose, and they could have chosen to refuse the serpent. However, God, having created the serpent, Adam, and Eve, knew what was going to happen by virtue of His intimate knowledge of His creation coupled with infinite intelligence and wisdom.
It's the tension between Free Will (Choice) and predestination that I'm questioning.