You've touched on a subject I've struggled with understanding, namely, where to draw that proverbial line. One thing I can say is just because God knows (decrees/allows) what will transpire it doesn't affect the choices we make. They are perfectly free and therefore we can be held responsible for those choices.
I'm pretty dubious whenever I hear people point to our genes. It seems like a genetic scapegoat, you know, "It's not my fault, I was just born that way." As to our social conditioning, this does make more of an impact. Just looking at how abusive parents can damage their children is just one example. But even then, we have seen people overcome those circumstances. We even applaud them for their courage, strength, or faith.
So really, it still boils down to how we choose to act. And God, rightly, holds us to our actions. He never made us sin. But apart from His grace we would still be bound to sinful natures, never being able to seek what is good.