For this reason, I have never been all that impressed by the "refutation" of the first cause argument; the refutation being that it supposedly requires a complex "first cause" God, Who is Himself in need of explanation. God could conceivably have been simple (as simple as a Big Bang, anyways) and then developed (some people would prefer to say "evolved") under His own internal dynamics into something much more complex. Just as we atheists claim happened to the physical universe.

That simple "God" is the "God" of evolutionary theory. The "first mover" theory does require a complex first cause. It was made in ignorance of evolution, and assumes that a complex design requires an intelligent designer. Every last one of the defenders of the design theory denies that what you say is possible.