I think the greatest damage done to humanity by religion, is the concept of original sin. To be sure, we are all flawed. Nothing is perfect, nor should it be. But that is not the same as the idea that we are all born unworthy, requiring of forgiveness by some divine being.
This concept isn't exclusive to Judeo-Christian beliefs. Almost all religions contain some facet of this idea. The folly of basing one's life on the fear of eternal damnation became obvious to me early on. It's a scam. Not even a good one. We were told that we had a disease, and that God was the only cure. Later on, as the lie gained more power, we were told that we had a disease, and if we didn't take their cure and tell everyone how great it is, we'd be tortured and killed. Why wait for damnation?
Even today, there are politicians in this country that would have no problem bringing back the Inquisition. We are so saturated by batshit crazy, that it's now become the new norm.
Consider, a newborn has no capacity for good or evil. Both are things that are learned. A brand new human being is almost pure potential -- and a learning machine. The first year or two is spent establishing neural pathways, and beta testing the ol' pattern recognition software. In short, we observe.
If what we witness is hatefulness and stupidity, especially if actively reinforced later, then we tend to turn out hateful and stupid. Luckily, the opposite is also true. Of course there are exceptions. Randomness makes the universe interesting.
Original Sin is a get-out-of-jail-free card that absolves us of responsibility, and reinforces the scam. Kahlil Gibran once said that we are not completely blameless for the crimes done against us. This world is a collective reality that we are all responsible for. If there is too much evil, and not enough good in it, then it is not God's will, but our own.