"Sin" is a manmade concept created to control the masses. Sin leads to guilt. Guilt is a powerful tool used to lead people down a particular path.
According to the fairytale, we are all born into sin thanks to dear old great-grandpa Adam. Because of this we are all deserving of death at conception. There is nothing we can do to prevent this on our own.
Thankfully (sarcasm) dear old YHWH sent his own son to die for us miserable, good-for-nothing sinners. All you have to do is follow his commandments as prescribe in this book written by men and you'll be a-ok. If you don't, well then to hell with you!
Not only is sin ridiculous, but so is the concept of an entire species being doomed by the actions of one man. That is like locking up people in prison because their great-grandfather was a convicted felon and for no other reason.