> Morality can't be "that which contributes to human well-being", or else a guy like Hitler can slaughter 6 million Jews and say, "Hey, I just made the world a better place!"
He could say that regardless of how (or by whom) morality is defined. But he would be wrong because as you already know, a society that institutionalizes killing of people based on race is likely to reduce the well being of nearly everyone in it. To think that such a thing improves well being would require you hold false beliefs such as thinking that Jews are subhuman and are trying to destroy society. But even Hitler would probably have agreed that morality was connected to human well being. It was through false beliefs that he thought what he was doing was good for society.
The fact that morality corresponds to human well being does not mean that there will be a universally agreed upon answer to all moral questions. Nor does it mean that morality is somehow going to be magically enforced on people who choose to ignore it. But in these respects it is no different then where we would be under the theory that morality is determined by god.
> "Well-being" is too easily a contrivance of opinion is there is no reference point from which morality stems.
Well being is the only reasonable reference point because there is no way to demonstrate what god thinks about morality or what his rules are. Also the only moral rules that are generally agreed upon outside of any particular religion are all related to human well being. So even though the most accurate meaning of a word would not depend on whether it is "too easily a contrivance of opinion," I think that claiming god decides morality is far worse in this regard. Nobody can demonstrate what god thinks or what his rules are so under this model nobody knows anything about what I moral or not. It is totally dependent on each individual's beliefs about what they think god wants.
Under your model Hitler could simply say "God wants me to kill Jews" and there would be no way to prove him wrong. Under my proposed explanation you can actually show where he went wrong and explain why you shouldn't think he acted morally.
> Ironically, I would say in the context of this conversation, the whole point of the Bible is to reveal God.
But there is no reasonable basis for thinking that any of the authors of the bible had any information about god.
> This is spurious, unsupported, and illegitimate.
Well for example, we both agree that to have a healthy society where human well being flourishes it is not a good idea to allow people to own other people as property. According to the bible you can own others as property and there are numerous rules detailing the rules of such ownership. Following these rules decrease well being. So if god made these rules then he wants us to live in a state that does not maximize human well being. If you knowingly make rules that will hinder well being then I believe it is fair to call you immoral.