Spirit, soul - now you are talking nonsense again. There are no spirits or souls of any kind, anywhere!!! Grow up. - So said by God allowing the decision of your free-will soul.
If free will exists in your soul, does your soul exist in our deterministic world? Yes or no, please.
If yes, it is not free will because it must obey the deterministic laws of our deterministic universe.
If not, it cannot be the cause of anything in our deterministic universe. - In the universe, but not of the universe.
BTW, the same goes for your God object/concept, if it exists outside of our deterministic universe, it cannot be a cause of anything in this universe. If that is true, then there is no difference between your God object and any other object that does not exist. Lack of evidence supports that notion. - Outside of the universe, and inside of the universe, but not of the universe, except in the physical part of Jesus.
For the record, I am not convinced that our universe is deterministic. If you look at the quantum effects, it becomes abundantly clear that it is not. But please do not claim that God/souls/angels are the cause of non-deterministic quantum effects, because that would be another Christian heresy. - Nobody has proven quantum effect in nature without mankind making it... C&E.
BTW, the C&E regression can run ad infinitum. I see no logical argument that it cannot. Actually, it would be illogical to assume that it (God) started without a cause. However, the way our universe actually started, it is actually nonsensical to talk about a cause or effect in the absence of space-time. You need time to determine what is the cause and what is the effect. - You can't describe the qualities and attributes of God outside of the universe. What is C&E to us might be something completely different to God. But when God makes the universe, it becomes C&E to us.
As for our brain, it is an automaton; it responds to the environment, our actions are predicated on all the prior stimuli our brain received.
There is no independent free will, IMHO. There is an illusion of free will, but our actions, our thoughts are driven by what we have experienced in the past. Even when you make that final, split-second decision, it is made because of some last cause and the 100B neural network that processed that cause. - Another way to say what I have been stating all along. This means that there is no free will except if it is found outside the brain. "Outside the brain" can mean seeming to be within the brain, but outside of it "dimensionally."
PS. To answer your question. I do not believe in God because I have read all three Abrahamic holy books. It is clear that they were written by people to control other people. Writers projected their own personalities to the God they have created. It is fiction, a scientific nonsense. Moral rules listed in them are abhorrent. God is a psychologically comforting concept, but it has nothing to do with reality.
You talk about the Bible killing babies. But our abortions in the US have murdered way more babies than any holy book could ever think of killing. And our abortion clinics certainly aren't religious places in the sense of formal religions.
You might be a wonderful guy, yourself. But holy books are designed to get rid of the murders, even if it takes killing the murderers to stop the murders.
If you look in Ezekiel 18, you will see that God isn't interested in killing people. He is interested in getting rid of the killing. If the murderers stop murdering, God is ready to forgive and forget their past murders. And the same with their other evils.