I'll throw in a trap card
But, if we weren't evil before that, how could Adam commite a sin, even though he was purely good?
Because Adam didn't know it was a sin. God expected him to blindly do as he was told, and when he didn't God damned all humanity for Adam's insubordinance. Then thousands of years later, God got himself killed to save everyone.
(quick version that someone will surely protest against)

