Original Sin does not prove that Man is evil either, unless you misunderstand what Original Sin is.
Man was created with a body, a soul (life-principle), a spirit, and the indwelling of God, sanctifying grace. The nature of Man is the nature of man deciding what man can and cannot do.
Grace is supernatural. It is beyond our natures. We do not have even the tiniest seed of which we could grow it on our own. We get grace from God or we have not at all.
Adam was created with grace in his soul. Grace is supernatural life within him. Because he had this he had prenatural graces also.
But, he also had free-will. He chose badly and as a result, the indwelling of God, sanctifying grace, left him, and naturally, he lost the preternatural (???) graces too.
So therefore, what was left was Man, a body, a soul, a spirit, free-will. Basically man was left with nature only, the supernatural life died within him.
Original Sin does not state that Man is bad in his being. Original Sin only shows that man is left with nature only. As such, he is weakened however, not totally depraved. A baby is not evil.
So Christ had to come to give the supernatural life back to us, and we have to be reborn with it.
"Genesis 3 does not teach that man is now ontologically bad, bad in his being, but morally bad, bad in his choices. God made our being; we make our choices. Yet it is our state of sinfulness, or seperation from God (our state of original sin), that leads us to make sinful choices (actual sins). The word "sin" comes form the German 'Sunde', which means "seperation." We sin (actual sin) because we are sinners (original sin), just as we sing because we are singers. Sin is not our essence (that remains ontologically good), but it is more than our day-to-day choices, it is our habit, our charachter. Yet this habit or character in turn was cause by Adam and Eve's first "actual sin" or evil choice, symbolized by the eating of the forbidden fruit.
How are we to blame for what Adam and Eve did? We aren't; we are to blame for what we do. But what we do is conditioned by what they did, just as a baby who is born a drug addict because it's mother took drugs during pregnancy, is conditioned by what his mother did. The mystery of heredity is part of the greater mystery of solidarity, of interdependence among individuals, that goes all the way up into the Trinity itself.
The Bible never says we were punished for Adam's sin, but rather that we sinned "in" Adam. There is a mystery of solidarity. Premodern thinkers, less individualistic than we, saw the human race as an organism, like a tree, not an anthill. Each individual (leaf) gets bad sap because the tree as a whole has bad sap. It's not a matter of imitation, of anthill-like "follow the leader," but of incorportation, just as our salvation through Christ is not a matter of our imitating Christ from without but of being incorporated into Christ from within by faith and baptism. (It's all in Romans 6)."
You Can Understand the Old Testament - Peter Kreeft