I will prove to you that God exists

[Belacqua]

However, I do appreciate the argument that scientists need to explain the biofriendly characteristics of our universe if there is no multiverse.  I give Drew that much credit.  

I think that when believers like Drew attempt to find scientific evidence for the existence of God, it is like a compliment they pay to science, and our modern habits of mind. 

In our time and place, science is considered the best (or perhaps the only) way to know about the world. When Christians then attempt a fine-tuning argument, or some pseudo-scientific intelligent design argument, they are attempting to use the tools of the modern world. They are saying, in effect, "only science will persuade you? OK, I'll use science." But I think this will never succeed. 

Science, obviously, uses methodological materialism as its foundation, and that is just not the right approach for metaphysical questions. Science works really really well precisely because it doesn't attempt to answer metaphysical questions. But that also means that if we're going to work on metaphysical questions, like the existence of God, we have to use different methods, and different standards of evidence. So bringing up multiverses I think is just irrelevant. 

As usual, I want to contrast some modern Christian's attempts at science with a more purely metaphysical system. If people are talking about the God of classical theism, then they would never expect the kind of evidence which modern people, accustomed to scientific questions, would find persuasive. In the classical theistic view, God is "is immutable, impassible, transcendent, and entirely self-sufficient. This understanding of God emphasizes divine simplicity, where God's essence and existence are identical, making him fundamentally distinct from all created beings." No material evidence of such a God would be possible. Methodological materialist approaches would not address the issue. 

I do very much agree with you when you say "We have abandoned the God-concept for a number of other reasons, and God is an uneconomical hypothesis to explain either the big bang or the specific characteristics of the universe which actually resulted from it." [emphasis added]

Thinking adults who are atheists, who have considered and rejected the claims made by Christians, are atheists for reasons. Their atheism is not simply a lack, but a considered conclusion, based on what they consider to be standards of evidence. The lack of evidence has been asserted repeatedly on this thread as the reason why one has no belief in God. A thinking adult is an atheist because he concludes that there is no persuasive evidence.

(If some atheists want to argue that they are NOT thinking adults, that they have no standards for evaluating claims, and that their atheism is exactly like that of rocks, lizards, and new-born babies -- simple, trivial lack -- I guess they could do that. But it would not speak very well of them.)