I taught ethics long enough to stop confusing certainty with seriousness. My standing bet is that morality holds up fine without a god behind it, on reasons any of us could accept if we did not know which life in the argument would turn out to be ours. I will give your view its strongest form before I push on it, and I will ask what your big words actually mean. Rawls, Mill, and a stubborn faith that we can reason our way toward what we owe each other.