But if all of society just innately ‘feels’ or ‘reasons’ that the same morals are good and right, why does there need to be some transcendent God decreeing it so—and why is such an external decree necessary?
Becasue if "everyone" "feels" this way it is either becasue a transcendent God put that feelilng there (which means consequences for disobedience) or it is merely an evolutionary survival characteristic. If it is merely an evolutionary social survival characteristic there would be no objective reason for any given individual to agree or feel bound that this feeling was "right" or "good". Why should anyone let others "feelings" interfere with maximizing their enjoyment of their very short life. If lying, stealing, killing and raping are what maximizes my enjoyment of life what would make that "wrong" regardless of how others "feel"? The big fish eat the little fish. It is what it is - whatever is, is right. Certainly "reason" can't lead to ethics because there are often very logical, rational reasons to do what others don't like in order to achieve your goals. If there is no God there there are only two laws:
1. Do as thou wilt; and
2. Avoid negitive consequences (ie. don't get caught)