Dont you get it? Under your way it is nothing more than a group of people making up a definition. It has no grounding outside the human mind.
It is no different to a flat earth society, they just define the earth as being flat.
The flat earth society believe something about an ontologically objective fact and they are wrong. That is quite different than people believing an ontologically subjective but epistemically objective fact.
And morality is not just a definition made up by a group of people on a whim. It was determined by something that transcends any individual or any group, i.e., social evolutionary imperative. That is what it is grounded in, not in personal opinion or even fashion. If a human society thought it fashionable to murder that wouln't make it morally right, and that society probably would not survive long.
Consider this.
Rostos believes big foot exists.
It is a fact that Rostos believes big foot exists.
Does that make it a fact that big foot exists?
Of course not, but that is a bad analogy. I already gave you much better analogy: I believe the United States exists. Of course, it doesn't exist because I believe it does, but neither does it exist ontologically objectively. It exist as a social construct. But as such there are epistemically objective facts about it. Moral facts are not exactly the same as that, but pretty similar. That killing people for fun is morally wrong is an epistemically objective fact based on a social evolutionary determined social construct called morality, with a fundamental principle, i.e., reciprocity.
So therefore under your world view, morality is merely a man made invention. Is that correct?
Not really. I mean human morality is to some extent man made, but other social species also have societies that apply the principle of reciprocity, though they of course can't articulate it in language the way we can. Again it is a matter of social evolutionary imperative not personal opinion or even fashion, at least not at the fundamental level
You are importing standards here such as reciprocity, justification. I don't see why in a naturalistic world how these are objective.
.
They are only objective in the epistemic sense that they are not a matter of opinion or fashion. They are not mind-independent though. They are ontically subjective (mind-dependent)
It doesnt have to solve every dilemma. You just have to show 1. The bible doesnt advocate moral absolutes, rather objective morality.
The OT passages for homosexuality regarding punishment no longer apply and havent fr 2000 odd years.
Not sure what you mean by I have to show 1. What I have to show to defeat the moral argument is that there is nothing incoherent about moral truths (or even just apparent moral truths) on naturalistic assumptions.
Of course, that doesn't prove morality isn't God given, just that the moral argument doesn't show that they are.