>So the atheist usually takes something non-absolute and makes it an absolute
Okay, so that's a basis. The only issue here being that you don't consider a non-absolute basis to be valid. However, the deity of choice isn't absolute either - you have to deem it so in the same way that the atheist does. So either way there's no perfect ontological solution provided by either path.
Well, it's not just me. A lot of people have, going back at least to Plato. Plato thought that you needed to have something absolute for there to be morals, but his problem was that his gods weren't big enough to proved that.
> However, the deity of choice isn't absolute either - you have to deem it so in the same way that the atheist does.
Yes and no. Yes, you have to deem the Christian God, say, to be absolute in order for Him to provide an absolute basis for your morals. (This is true whether or not that God exists.)
But the Christian is not in the same position as either Plato or the atheist. Within the Christian's position, God is absolute, and therefore can provide a rock-solid basis for a moral standard. In contrast, Plato's gods were inadequate as a moral basis, both in theory and in practice (that is, in practice they often behaved in ways that were not very moral).
The atheist has an absolute (at least, I think most atheists do) - the physical universe. Within (most flavors of) atheism, that's the only thing that can be really absolute, but it provides no moral standard whatsoever. (C. S. Lewis remarked that "what the universe is doing" is working toward the final and irreversible extinction of all life forms, and taking that as a moral standard would leave suicide and genocide as our only moral values. It seems better to just say "there's no moral standard there".) The atheist can pick a different basis for a moral standard and ascribe validity to it - say, the human race, or the atheist's society, or whatever. But the atheist has made a somewhat arbitrary choice - there's nothing within the atheist's position that compels that particular choice of moral basis. What's more, the atheist knows it. This is very different from the Christian's position, where there is one clear moral basis that can only be accepted or rejected.
> But the Christian is not in the same position as either Plato or the atheist. Within the Christian's position,
Yes, the position they just chose. It's like saying after you've made a choice, you can either take it or not
I wasn't intending to, but perhaps I should have been. A Muslim has the same situation as a Christian - somewhat different morals, but the structure of the situation is the same. The distinction I was drawing was between polytheistic gods and a monotheistic, absolute God.
> Yes, the position they just chose. It's like saying after you've made a choice, you can either take it or not
I see the "choosing the Christian position" as parallel to "choosing the atheist position". But my point is that, when you choose the Christian position, that defines morals for you. When you chooses the atheist position, that does not define morals for you.
The parallel to "choosing the atheist position" would be "choosing the theist position," which would not define your morals either. From there, you can choose from a massive range of Christian positions which have different morals.