Two points.
Occams Razor. So yes, I'm going to say "what caused God?". There is an equal amount of evidence for Big Bang theory, and Big Bang theory + God, so you take the simpler theory, which doesn't include God.
Second, it doesn't matter whether the Big Bang or any other explanation for the universe is supported by the evidence or irrational. What matters is, is God supported by the evidence. I have yet to see any evidence in favor of God, so therefore, I don't believe in it. It's irrelevant whether any other explanation fails. In the case of no explanation being good enough, then the logical choice is to say "I don't know."
Perhaps there's an equal amount of evidence for both God + Big Bang and Big Bang by itself (granted for the sake of argument, not because I agree with the premise), but it does not follow that Big Bang alone is the correct theory. In this case, I believe that the implications of Big Bang alone make it more complicated than God + Big Bang.
The implications, as I see them (as always, correct me if there's a flaw in my logic) are as follows:
1) The universe is self-created and self-sustaining. Yet no other system or individual that we have yet seen is both self-created and self-sustaining. From a purely inductive basis, this is incredibly unlikely.
2) If this universe caused itself, there's absolutely nothing preventing several other universes, in fact, infinite numbers of universes, from causing themselves as well, requiring some sort of multiverse theory, and multiverse theories, from cosmologists to Marvel Comics, are universally agents of immense complication.
So yes, Occham's Razor indeed: I choose God as a simpler explanation than self-generating universe + multiverse. By definition, God is self-existent. This means that he is not contingent upon anything. The Cosmological argument is intended to prove that the universe is contingent upon something, as it began to exist. Thus, the simplest explanation is to assume that the universe is contingent upon one non-contingent being.
The argument needn't be direct evidence for God; it can merely contribute to our understanding of the universe. In its purest form, it simply states that something must have caused everything else, and that thing must be un-caused, and excludes the universe as a possibility. It creates, if you will allow me to borrow from Augustine, a God-shaped hole in our cosmology (hmmm... we need an eternal, uncreated, immaterial being... hmmm, what shall we do...?). Yes, it does not necessarily prove that it is the Christian God that fills said hole, but surely you can allow that a given argument affects our metaphysical outlook, and that in turn our metaphysical outlook can make the statement "God exists" appear more likely than the statement "God does not exist"?
And once we get to that point I'm too lazy to figure out how to counter skepticism (the actual epistemological position, not the regular use of the word) right now, except to say ask for what reason does one not choose the most likely solution rather than to stay indifferent (crappy argument, I know. Maybe I can talk to some people smarter than me and go at it again later).
Argument from authority. Many highly intelligent and respected people throughout history have supported the concept of God, but that doesn't mean anything. Only the quality of the arguments does, and the quality is not up to par.
The claim that tradition means nothing is an obvious overclaim, but you're right, you totally caught me in that particular fallacy. I'll read up some and try to present some actual arguments.
Or perhaps,
(7) A being that of which no greater being can be conceived, does not exist.
I can conceive of God being omni*insert stuff here* (even if not the mechanisms). I can also conceive of God existing. If in step one, you conceived of an omni*insert stuff here* being, yet failed to include the existant part, then the argument "works", but only because you were incomplete in step one.
Hmmm... okay, then, how about the Cartesian update:
1) A perfect being has every perfection
2) Existence is a perfection
3) Therefore, a perfect being is, by definition, actual, rather than possible.
And yeah, Beauty of the Infinite is a wonderful book, from all I've read. He argues that Christian rhetoric inevitably resorts to beauty as "proof," and then says that Christian rhetoric, unlike most rhetoric, is loving rather than violent... it's very complicated and I'm not doing him justice here. It's a lot like poetry; the paraphrase is entirely insufficient to the actual thing.