Emphasis mine. That is the crux of the matter. It is ironic as you state with respect to an objectivity devolving into subjectivity. Since we are all human beings, by our very nature we will have morals, morals of great difference ranging to similarity. It is a basic human condition, and cannot be ignored.
Yes. That is the crux of the matter. In my opinion, the Fall is precisely that. The devolution from objectivity to subjectivity. Whether you see it as beginning with Adam and Eve or simply the result in each individual of making the fundamental decision to say, "I am smarter than God," the result is the same.
You're exactly right, by our nature we will have morals. It is the condition of fallen man. I suspect, that unfallen man does not even have to raise the question.