This is so interesting! The organization I am the president of, the Apologetics Research Society, put on a debate on this exact question a few years ago. The one arguing that God does not exist was Michael Shermer, who is the president of the American Skeptics Society. Shermer through out a lot of rhetoric and funny one-liners, but the bottom line of his argument was the burden of proof argument. In other words, he said that unless we can prove that God exists, then we ought to assume that God does not exist. Mr. Shermer was utterly defeated in the debate by my good friend Dr. Douglas Jacoby because he did not fall for this bogus (in my opinion) argument. By the way, you can get a copy of the debate at www.ipibooks.com
Who says that no God is the default argument? By the way, I believe that there are some arguments in which default arguments are valid. For example, when it comes to the resurrection of Jesus, we know from science that resurrection is seemingly impossible. Like David Hume said, extraordinary claims require extraordinary proof. I can buy the claim that, when it comes to the resurrection or to the inspiration of the Bible, the burden of proof is on the believer.
But with the existence of God, I definitely do not agree with this at all. The bottom line is that the vast majority of all well-educated, experienced and wise people in human history have believed in some sort of Creator or supernatural presence. Why ought the belief of most of these people be assumed wrong, simply because the majority says it should be assumed wrong. We have to explain the existence of the universe somehow. It seems obvious to me that there is a Creator. But even if I am not right, to say that no-God is the default argument is simply bogus. It amounts to making no argument at all. Like I already said, I believe that there are real questions for which a default argument has at least some validity, but certainly not in the argument about whether there exists a supernatural reality.
By the way, atheism is a worldview. You should not say this. Everyone has a world view, and surely there are people who hold to a wordview which, at the very least, includes atheism. Perhaps you can give it another name such as naturalism or determinism if you like, but I disagree with the statement that atheism is not a worldview.
I kind of like your detective analogy, but I am not sure it is a perfect analogy. If I say that there is no evidence that suspect A did the crime, that does not mean that I have to have another suspect. If suspect A was in another country at the time, then, as a detective, he is eliminated as a suspect, even if I do not have another suspect. To be honest, I think that the “burden of proof” argument does in fact apply to crime investigation. The burden of proof is on the one who claims that the suspect did it.
A fun question!