First, be careful with citing things like being corrupted by sin. We're still arguing about whether God exists at all, and you shouldn't be interjecting evidence based on you specific theology.
Second, omniscience is an interesting concept to bring up. In the sense that God would know for a fact what a person did, and why they did it, He would be a better judge of course. For instance, I can't be certain that even O.J. did it, to quote Bill Maher. But in discerning whether a concept is moral or immoral, sure, having an omniscient being that can look at all the pleasure and harm that results from an act would be the perfect way of discerning right from wrong. But doesn't this mean that the more we know, the better we can discern right from wrong? I mean, sure, we're no where near omniscient, obviously, but the closer we get, even if only a little bit, the better we can discern.
The advances we've made in psychology and neuroscience can actually show real physical changes, such as electrical activity in our brain, and the release of chemicals and hormones based on our actions, the actions of others towards us, and stimuli we receive. Sure, it isn't practical right now to test these things as people go about their everyday lives to truly measure them exactly to show how much harm is done or pleasure is received by different acts. But who's to say we never will? People used to think it was impossible for humans to fly. In the meantime, we can use the data we do have to make generalities about things that have a lot of predictive power about how people are going to feel and act and help us to find things that are moral or immoral and why we do them.
And just for fun, I'll break my own rule that I started this post by stating that God said about the tower of Babel that nothing is impossible for humans if we all work together. I don't consider that a real argument for anything, just food for thought, you know?
That's fine, it makes more sense now.
