I think I hear ya correctly - Cain knew that he had committed sin when he killed his brother Abel ~ there wasn't any written revelation at the time. (Genesis 4)
But for me the narrative doesn't end there, while I believe we have an inner blueprint, I really do, God was also merciful to give his people the "Law of Moses" that they a sinful people could come into contact with "Holy" - and His people still dropped the ball, thinking they could be "holy" and stand in His presence by sacrificing helpless animals or by eatting and cleaning themselves correctly.
Now, I also know that Christianity in the USA is also a lot more "political" than here in Canada and that has turned more than one stomach both on the outside looking in but alos on the inside looking into Christianity. I have done some of my own research into Deism, and while I cannot disagree that there is a blue print or more, I cannot fathom a rational for why there isn't any "revelation" from this creator ~
If some "Law" wasn't written down we would have what we read in the "The Lord of the Flies" - accept there would be no rescue -> Piggy's out there would all be dead -> because they are dying anyway with the blueprint and the revalation
But I won't be the guy confused with having blinders on either. I see the inflexibity of Christiniaty, I talk to people, and that is why I always return to Jesus and what Jesus had to say over anyone's cherry-picked story or account. Yes it gets me in trouble, as did coming out of the closet.