We are told two things by Christians. 1) That we live in a universe fine-tuned for us and 2) we are all sinners.
The irony of saying that we are in a perfect universe but that it can't allow for that one variable is beyond them, I guess.
Anyway, sin is the glue that holds christianity together. It is the common denominator that makes for obedient denominations. It is the fear factor that is used to control and uninform the masses. It is the hole card. It is the cat's pajamas. And Christians love it. They wouldn't have it any other way. Christianity without sin would just be no fun at all.
When you can have one thing, sin, that can both hold your group together and justify denouncing others, you don't even have to run around inventing a second concept. Its a one size fits all idea that can be conveniently corrupted as necessary, and also be defined as something personally humbling, if that is all you need. It excuses frightening kids and works really good as a hammer to hold over anyone else who dares cross your path.
In other words, technically speaking, it has been made to be more universal than the universe itself.
Christianity wouldn't be able to exist as invented without sin. It had to be introduced early in the story, after implying that perfection would have been possible if only our lady friend hadn't acted so impulsively. Perfection was around just long enough to be alluded to. The lack of details was purposeful. Since it is a bit too hard to go into perfection in any detail. It can't exist. And the fathers of the church had to allow for that. The bad had to be kept in the forefront, for all humans and all situations. There is no reality that can't be defined as sinful by someone. Had any more detail been provided about Eden, people would have seen that it wasn't so great either. Humans can only hint at perfection. The church fathers played that one to the hilt.
The job of sin was (and is) to justify the religion. Viable alternatives would ruin the whole thing.
We can look at the Christian reality as a sandwich. In the middle is us, sinners extraordinaire. One slice of bread is the alleged perfect state we all abandoned when grandma Eve erred so grievously, and the other slide is the return of JC. To keep people from fretting too much, this sandwich of has a slathering of heaven on it, just to keep the infinitely long waiting period between the two pieces of bread tolerable. That allows for all variables, as defined by the church. Which are 1) a long time ago and 2) the future. Or the prospects of heaven/hell, if one should be so unlucky as to die before the Jesus character reappears in their story.
So the myth we atheists are fighting when we take on Christians is not their god. It is their excuse. And that excuse is sin. We've been dong it wrong. It's time to go after the disease, not the symptom. The naïve notion of sin needs to disappear first. The normal range of human behaviors has to be redefined as normal, not as a personal affront to their god. IF we can succeed in that, the church will have no justification for existing.