a non-believer will talk about what God says... and point to passages in the bible wherein God does something that strikes them as abominable
That is because you would likely see those things as abominable too.
At first blush, yes. It's a completely understandable default reaction based on where and when we live, but based also (amd most importantly) on the belief that we can determine what is good and bad without deferring to any absolute moral authority.
I have a hard time when people read the OT bible and are not horrified. It really makes me wonder whether they are sane or moral.
What is moral, though?
You are not judging yhwh on his actions. You are viewing yhwh through a lens of preconceptions.
And you're viewing Him incompletely, as someone whose actions can somehow be legitimately challenged by a creature it created.
A plain reading of the OT portrays yhwh as an abominable character. Early xians - gnostics - saw this too. It's not just us.
It portrays God as being utterly and completely incapable of co-exisiting with sin. Which is certainly depressing, until you read the NT and see how God dealt with the problem, once and for all, for anyone who cares to admit the problem and have it dealt with.
if God really exists, He created all life,
So what? An evil god could create life. Maybe you have just been duped by his PR team?
I guess nothing is impossible, theoretically. But my experience has always been that experience kicks theory's bum every day of the week. My experience is that God is good.
and is the only possible ultimate authority.
You've said it, but not demonstrated. I consider things like concepts and natural laws to be authorities. Gravity is an authority. The say so of bigger people, not really ultimate.
But, again..we aren't talking about people, and the problem of "partial God" arises. The God of the bible set those natural laws you like into motion.
How can a created being tell its creator that it is wrong?
I depends. For one, if the created being was created with the capacity to know and the creator had the capacity to be wrong. Remember, when speaking of morality, we are yhwh's equal. Eve at the fruit of moral knowledge. So, that is another way.
That's an intereesting thing to dwell on, actually. The bible tells us God was sorry he'd created mankind at the point just prior to the flood...but I'm not sure that means He was wrong. I'd give an analagy but I know you dislike them.
As to the tree of knowledge of good and evil, God warned Adam and Eve not to eat of it or they would die. They did eat of it, and it did bring death and knowledge, but that doesn't mean mankind were suddenly equal with God. It had the opposite effect, removing us from God. That was the lie Satan fed them that was swallowed hook, line and sinker. It's his most successful lie, been working ever since.
How can the creator of life not have the authority to end life?
You need to make a case that a creator has authority over sentient creations, not just defy us to show it doesn't.
Through Christ God demonstrated He has authority over not just sentinent creatures, but over death itself. The case is made to my satisfaction, not to yours.....we know this.
I do not understand how xians argue that human life is so intrinsically valuable and then turn around and view it as a posession.
God sees us as valuable. He chose to create humanity. That's the only way or reason our lives have intrinsic value.
If morality is real, then it applies to everyone, even god.
Maybe the theoretical God you have in mind. Not the God of the bible.