Christians are always trying to absolve God of moral culpability in the fall by whipping out their favorite "free will!", or “ it’s all man’s fault”.
That is "God gave us free will and it was our free willed choices that caused our fall. Hence God is not blameworthy."
But this simply avoids God's culpability as the author of Human Nature. Free will is only the ability to choose. It is not an explanation why anyone would want to choose "A" or "B" (bad or good action). An explanation for why Eve would even have the nature of "being vulnerable to being easily swayed by a serpent" and "desiring to eat a forbidden fruit" must lie in the nature God gave Eve in the first place. Hence God is culpable for deliberately making humans with a nature-inclined-to-fall, and "free will" means nothing as a response to this problem.
If all sin by nature then, the sin nature is dominant. If not, we would have at least some who would not sin. That being the case, for God to punish us for following the instincts and natures he put in us would be quite wrong.
Psalm 51:5 "Surely I was sinful at birth, sinful from the time my mother conceived me."
Having said the above for the God that I do not believe in, I am a Gnostic Christian naturalist, let me tell you that evil is all human generated. Evil is our responsibility.
Much has been written to explain what I see as a natural part of evolution.
First, let us eliminate what some see as evil. Natural disasters. These are unthinking occurrences and are neither good nor evil. There is no intent to do evil even as victims are created.
Evil then is only human to human.
As evolving creatures, all we ever do, and ever can do, is compete or cooperate.
Cooperation we would see as good as there are no victims created. Competition would be seen as evil as it creates a victim. We all are either cooperating, doing good, or competing, doing evil at all times.
Without us doing some of both, we would likely go extinct.
This, to me, explains why there is evil in the world quite well.
Be you a believer in nature, evolution or God, we should all see that what Christians see as something to blame, evil, we should see that what we have, competition, deserves a huge thanks for being available to us.
There is no conflict between nature and God on this issue. This is how things are and should be. We all must do what some will think is evil as we compete and create losers to this competition.