Let me start with this, up front:
The fact that I'm having this discussion with you at all ought to suggest to you that I'm interested in your position. There's no need for you to get defensive about it. It isn't that I'm unwilling to consider your line of reasoning. To me, it seems more like a case of you being unwilling to share it with me in more detail. Ability is a different question. It is conceivable that you're much smarter than I am, so that I won't be able to understand your reasoning. But we can't really know that unless you try to explain it to me.
You also seem to be under the impression that I have not "reasoned it out for myself". For my own part, I would say that I have spent quite some time thinking and reasoning about these matters. As a result, I have come to some conclusions of my own. That's not to say that I couldn't be wrong or that I have nothing else to learn.
If you regard your own reasons as too personal to discuss, or something like that, I understand. We don't have to have the discussion if you'd rather not. The same goes if you don't want to put in any more effort to explaining your position. You can certainly leave me to continue to "reason it out by myself" without your input, if that's what you prefer.
Moving on...
That wasn't meant as defensive at all. I'm literally asking you, to see if you come to the same conclusion I did, without me biasing the result. If you have already reasoned such things out for yourself, I'm genuinely interested to know your conclusion. I assume my reasoning could be reached by others, and it is in no way personal. But I am not the one in need of convincing here. You are. And as such, there are points where you opening the door yourself is much more compelling than anything I could hope to convey second-hand.
At least, you've talked as if you were genuinely open to being convinced.
You say there's no other explanation, but is that true? It sounds to me like you just have a preference for one explanation over others.
Then what other explanations are there?
The other issue I have with this is: why assume anything? Why assume there is a God, if there's no good reason to do so? Why not just be content to say that we don't currently know why there is something rather than nothing. Maybe we'll find the answer in the future. To me, it sounds like you're pretending you know the answer already, when you don't really know at all.
Again, if there are alternatives to just throwing our hands up, I'm all ears. Not in my nature to just dismiss hard philosophical questions. Many conclusions we have not come to ourselves sound like pretense.
Again, the problem I have with that is that I think it makes "God" just a synonym for "everything" or for "existence" or whatever. Why use the word "God", when we already have the words "everything" and "existence"? What value does God add to this worldview?
Does belief in existence alone add anything to life? Considering the success and freedom of things like the US is predicated upon Judeo-Christian values, God seems to add quite a bit.
I agree that our universe had a beginning, with the caveat that we don't really understand how time works in very earliest stages of the big bang. You say that we have zero reason to think that a multiverse wouldn't have a beginning. I say we have no reason to think that it would.
So you're fine with infinite regresses? You've yet to explain how an infinite regress is not fallacious.
As for lack of evidence, we agree that my lack of evidence for a multiverse is on a par with your lack of evidence for God, don't we? So, we can't decide between those two hypotheses on the basis of (currently available) evidence.
Of course, with the addendum that only one hypothesis makes claims of possibly having physical evidence.
A multiverse obviously wouldn't be, either.
A multiverse is just a collection of physical universes, with possibly varying laws of physics.
I'm not sure how familiar you are with ideas about multiverses, so forgive me if I'm telling you something you already know. Not all multiverse ideas require consistency in the laws of physics. Some multiverse ideas posit the idea of "bubble universes", with each causally-separate universe containing its own set of physical laws (or at least its own group of "settings" for such laws, in the form of fundamental constants such as the strengths of fundamental forces in the universe). Using such ideas, our universe could just be one of an uncountable number of possible worlds.
I'm familiar, but not sure what that has to do with the relation of God to this or multiple universes. A God could just as readily create a multiverse, with each being a laboratory for different natural laws. My mention of the consistency of natural laws would then only apply to each universe individually. So I'm not sure how you think a multiverse is competition for the idea of a God.
As for subjective experience, I have no reason to think that our subjective experience is grounded in anything other than physical reality.
As for free will, my views on that topic are on the record elsewhere on sciforums, at length. To summarise briefly: I don't think that free will requires the presence or intervention of a deity. Tentatively, I don't even think it is incompatible with determinism. And I disagree with your position that free will cannot be explained from a materialist perspective.
I have no reason to think that our subjective experience arises solely from our physical bodies. Otherwise, some experiment should have illuminated that terra incognita by now. Likewise, I see no reason to think that we have no "genuine ability to do otherwise", although I think that requires deterministic cause and effect. The only experiment that seemed to show our perception of free will was illusory, Libet, was fairly recently debunked. Believing science will do things we have no evidence it may do is scientism, but your prerogative.
Do you believe that our thoughts and/or feelings require something other than physical reality to account for them fully? Do you believe, for example, that God is needed for human beings to be free, or to be conscious, or stuff like that? I appreciate that this is a silly question, in the sense that you believe that God is needed for anything to exist, which would include consciousness and free will necessarily. But do you think that free will or consciousness etc. is an especially good pointer to the existence of God?
We certainly do not, as yet, have a physical accounting for them. You can call that "God of the gaps", but how long must science go without answering some of these question without it becoming scientism, i.e. "science of the gaps"?