My main argument is that God is the natural world together with an opinion about the natural world (that it is ordered). If you think this is unjustified, what property must God have that this doesn't have?
It seems like this is a problem with semantics. What you are calling "God" is in no way related to the Christian or Muslim concept of God. Instead, you are applying the word "God" onto what a non-theist would call "Nature" or "The Universe". In reality, it is not a belief in God at all, but simply a label you have applied (or perhaps misapplied) to something else entirely.
Now, I have only read about the first 25, and last 60 or so comments on this topic, so if I missed something that pushes your belief into a more theistic direction, please correct me. So far however, I have read very little that leads me to assume you are holding a theistic belief in "God".
Then the example is pointless. A weapon powerful enough to cause extinction galaxy wide is a very big if. It's unlikely there would be, simply because of the massive distances between stars.
Also, if you base your argument (or part of it, anyways) on such an event, it is equally fair to state "if not". And in the case of "if not" (which I imagine to be highly more likely), the argument must end there.
Therefor, it is likely to assume that yes, we could outrun our own destructive tendencies.
At that point in our evolution we had no firm grasp on what "world" even meant, let alone a basic understanding of scale. Now, we do. We also have a basic understanding of the universe, and a method to increase our understanding (Ability to postulate theories, run experiments and collect evidence). When all humans (most likely an ancestor) were contained in one geographic coordinate, none of these things even existed as concepts. There are a few more problems with this comparison, but I'll leave them alone for now, as it does nothing to bring them out.