I think you are on the right page. Let me offer one bit of clarification and you tell me. First, we'd have to flesh out what we mean by "ultimate good." I'm not talking about God being an example of goodness for us to follow. I'm saying that Good
is God. You don't take this thing called "good" and predicate it to God. To do that would just be to say, "God is God." In fact, when we talk about good, we're really talking about God, even if we don't know it.
That "even if we don't know it" is the important part. The problem with atheism isn't that atheists don't have and don't believe in OM. They do. It's that they cannot rationally
justify their belief in OM. They can't give it an ontological foundation. To use another crude illustration, suppose you and I are drinking from the same stream of water. I say ask where the water comes from, and you pull out a map and show me that there is a local reservoir that this stream flows from. Now suppose for whatever reason I don't believe you. So you ask me where
I think the stream comes from, and at the end of that conversation, it's apparent that I just don't know. Wherever it comes from, I just don't believe it comes from a reservoir!
Now, supposing you were right, does the fact that I don't know the origin (or even deny it's existence) of the water mean that I am going to die of thirst? That I can't drink from it?
Of course not. It's the same way with OM. You believe in it. You rely on it. You assume it. And lots of atheists even insist on it. The problem is that you don't have a rational justification for it. What you are doing, without realizing it, is "borrowing" from a theistic worldview for this particular part of your belief system.
So shy of introducing some other ideas that atheists are very uncomfortable with (i.e., Platonism), the problem is that those who deny God (and His simplicity) they have
no ontological foundation for their belief in OM. OM can
only be coherently understood in a theistic worldview--and then, just any sort of theism is not enough. Islamic theism, for instance, doesn't work, and nor does the theism of Hinduism (which is more pantheistic), and nor, for that matter, is the theism of much modern evangelicalism. You have to have the theism of the sort that understands that Good is what God is; that God
is His essence (of these, Islam is the closest, but it gets off track for theological, not philosophical, reasons). That's the divine simplicity that Byblos was talking about before.
edit:
LIGHTBULB!: Maybe this would help (you or anybody else). Let's assume one horn of Euthyphro. Suppose things are good or bad because they adhere to some standard, some property, called "Good." Now, the ONLY way in ANY worldview that morality can be
objective is if this property, this standard, has
real, extra-mental existence. (That's what "objective" means.) What Byblos is saying is that the reason Euthyphro doesn't apply to God is that God is not a thing like you and me that has to appeal to that real standard. That standard
is God. Just "picture" that property--Good--and call it by its proper name: God. Just like it would make no sense to say, "We call something good because it measures up to the standard of Goodness; and the standard of Goodness says it is good because it sees that it is good" (if that's not obvious why that's silly, it is because it sets up an infinite regress), in precisely the same way it makes no sense to say "God says it is good because He sees that it is good."
So the real problem here isn't the question of whether God exists. It is whether or not Goodness
really exists or if it is just a human (subjective) construct. If it really exists, then we note that Goodness is what Christians call God; so the question becomes, are they right in that? Is Goodness identical with the God of Scripture? But by that point, we've moved well beyond the OM debate. The very admission of OM is the admission of God's existence. Now we just have to continue on down the road of finding out what it is that we can know about this God.
Of course, you can just deny OM, which is what most atheists end up doing. Then you would just be like me saying the reservoir doesn't exist. You'll still go on and live as if it does exist--you'll still believe in it and rely on it.You'll still enjoy the benefits of it, because it is just as much a part of reality as gravity. You'll just be wrong (and intellectually dishonest, insofar as you are living as if something is true that you have declared that you believe is not the case!).
I regularly recommend people read
this paper when having this conversation. It's well written, easy to follow, and introduces these concepts rather well. It also has the added benefit for you (an atheist) of giving you a better argument than that absolutely asinine, embarrassing attempt at an argument that Richard Dawkins attempted to use in his
God Delusion. What Dawkins didn't know what that his argument is nothing but a rather poor rip off of an actually good--indeed,
strong, in my estimation--argument against theism. Obviously, I think the argument can be met, but I appreciate it because I think it effectively rules out much of the silliness many Christians try to use when they talk about God's nature.