Let this serve as a notice to let you know that what you opine from my referencing of that video, is in error. I do not affirm the existence of any deity simply because I am referencing its qualities and attitudes as accepted by the believers in such deities. My point in referencing that video was just this - to bring to light the morality of the deity under question - as to how a child-killing god can be moral. That is all. This should have been abundantly clear and your extrapolation is not only strange, but self-defeating as well. It brings to question whether you're capable of interpretation and comprehension at all, quite frankly.
Now why don't I accept deities as entities that cannot exist? Let us look at the First Cause argument - one of the cornerstones of the "explanations" given out for why a God must exist. What should the primary quality of such an entity be? It should be timeless - that is, time has no influence on it. What else? It cannot perform an absurdity that contradicts itself.
So, assume you have this God who always existed. How does this God, from its vantage point initiate anything if it has no reference to anchor that initiation on? What did God do to begin its first act? God existed before God began its act.
Next, we have the impossibility of a God which orders sequential events (create Universe, then destroy it, think of Creation, then go about to initiate it, etc - things that require a separation) to be outside the realm of time. If no time existed for God, then two events initiated by God would happen simultaneously - thus, God would have not yet created and created the Universe at the same moment. This is an absurdity.
Lastly, it's funny to see how anyone can assume that David's illegitimate child, made to suffer for a week with agony, and then have its life snuffed out of it, can assume that the child ascended into "heaven". This is what the Old Testament has to say about bastards:
"A bastard shall not enter into the congregation of the LORD; even to his tenth generation shall he not enter into the congregation of the LORD." - Deut. 23:2
First Cause is an interesting subject.
The Cosmological arguments are a family of arguments that seek to demonstrate the existene of a Sufficient Reason or First Cause of the existence of the cosmos. Defenders of First Cause have been Aristotle, Plato, al=Ghaziali, Maimonides, Anselm, Aquinas, Spinoza, Leibniz, Locke and many others. The arguent can be grouped into 3 basic types; the kalam cosmological arguments the Liebnizian cosmological argument from Sufficient Reason, and the Thomist cosmological for a sustaining Ground of Being of the the world.
Now, I will not go into other of these explainations but will deal with your narrow application of the cosmological argument supported by Einstein, Wilson and Penzias, Eddington, Smoot, WMAP, the second law....all pointing to a beginning, which is what I believe you were referencing. All of these scientist, and many more point to an undeniable conclusion that the universe BEGAN. Moreover they point out that the universe came to be from nothing. The Law of Causality which you reference states, "Everything which begins to exist had a cause. At that point of singularity, (that moment of beginning which we can take back to Planck Time, demand an answer as to what WAS that First Cause which gave rise to matter, energy, space, and time. What was prior to time which could be that first cause to bring forth the universe (approx. 10 seventyfifty subatomic particles) out of nothing. Remmeber Aristotle, upon asking 'what is nothing", he replied....."Nothing is what rocks dream about." In other words..no thing...no matter,...no space, to time,...no energy. Nothing! Well, using logic and reason we must conclude that something made a decision to bring something into being out of nothing, and therefore a personal decisionf was made (Persons make decision, not molecules) Something must have been incomprehensibly powerful to create the univere from nothing. Something must have been incredibly intelligent to have created order out of caos of that origin. Something must have been timeless to have existed outside of time (prior to the existence of the creation of time), or some would describe as transcendent of time. Now, I have not described these 'qualities', as you describe, from Biblical descriptions. These are characteristics derived from the conclusions from the studies of Einstein, Eddington, even Fred Hoyl, Wilson and Penzias, COBE, WMAP, Smoot, Jastrow, and many others. It is interesting to point out that these characteristics describing that FIRST CAUSE are the same characterics which Christian theologans have described for 2 centuries.
Regarding your question regarding the notion what God always existed. You must remember that time did not occur until that singularity. Prior to that singularity, and thus prior to time, God existed timelessly. Now, whether you subscribe to A-theory of time or B-theory of time the principle holds.
Now, I will concede that I am somewhat limited in my ability to understand with the comprehension which you demonstrate in your questioning. All I can say is I try to tell you the truth. I do find humor in one of your last sentences where you affirm the absurdity of how God would have created or not created the universe, while in the same breath denying his very existence. You might want to look up the term - ABSURDITY.
Oh, don't expect an answer anytime soon...a bucketful of invectives and insults, maybe, but an answer, and a sensible one...never.
PS. A corollary to your question: what did God eternally "do" before he began to do anything...hmmm?