Yes, we are need in salvation. Yes, man has a sinful nature but it was not that way from the beginning.
Genesis 1:31 - And God saw all the things that he had made, and they were very good. And the evening and morning were the sixth day.
So good, you answered your own question, although I would disagree that we all have a sinful nature. We have the nature that God gave us.
I understand what is described in books, but I do not really know what it was like in the beginning.