I'm often confused to whether we are discussing science (something that is testable and amenable to metrics) or theological beliefs (something that has earned the trust and confidence of man and amenable to human predisposition).
I think that GIA is engaging in something like
critical-theology. It's theology, since it accepts the Bible stories as a given. But it's critical, since it implicitly denies your own assertion that theology is "something that has
earned the trust and confidence of man". The argument there would seem to be with your word "earned". GIA is seemingly asserting that at least some aspects of religious tradition are on their face immoral and unethical, and hence
don't deserve mankind's assent. (I agree with GIA on that, btw.)
Clearly, in some measure, religious beliefs are subjective. But we only get there through the Principle of Sufficient Reason (PSR).
I don't understand that.
Leibniz's 'Principle of Sufficient Reason' says
"there can be found no fact that is true or existent, or any true proposition, without there being a sufficient reason for its being so and not otherwise, although we cannot know these reasons in most cases".
I'm sure that there are reasons why many people possess religious beliefs. But it isn't necessary for us to assume that the reason is the ontological existence of the object of their beliefs. I'm more inclined to attribute the genesis of religious beliefs to social and historical context, perhaps in concert with innate psychological predispositions such as the human tendency to anthropomorphize.
The Supreme Being... is not subject to the limitations of humanity. There is no concept of "Right & Wrong" that is applicable to the SB; only outcomes. Compassion and morality are human inventions, not supernatural enlightenment or devine guidance.
If this "supreme being" is imagined as being totally amoral, and if we accept that moral predicates like "right", "wrong", "good" or "evil" simply don't apply to this hypothetical thing, then that threatens to deny and subvert a central and perhaps indispensible portion of traditional theology. Theology wants to claim that its "God" is supremely and ultimately
Good, and in fact (so Christian Platonists would argue) is the form and paradigm of all the limited earthly goods that we encounter in our finite lives. God is supposed to be the defining source and final arbitor of Good.
The problem is that unless God is at least as good as we human beings are, unless our usage of the word 'good' to apply to God meets at least the minimal standards that we insist upon when we use the word to apply to people, it becomes meaningless.
God has to be at least as good as we expect other human beings to be, or else there's no point in calling God good at all.
And there wouldn't be much justification in worshipping such a God either. In order to be a suitable object of human worship, God would arguably have to be morally better than we are, and he certainly can't be human beings' moral inferior.
Imagining God as untouched by human concepts of morality threatens to make God indistinguishable from Satan. Is God's only advantage over Satan simply that he's supposed to be the more powerful of two fundamentally amoral forces? Is that the only claim that God has on man's allegiance?