Yes, I disagree with all of it.
I do not believe that we were all "one with God" at some point, unless by "God" you mean the nebula that our sun formed from, which contained most of the atoms that compose our flesh today. I would not consider that nebula to have free-will, though.
I also would not consider any of us to have existed at that point, either. I think we are somewhat of a "ship of Theseus" problem, because there's a debate to be had about when "we" really begin and when "we" really end. At some point during or after conception, molecules eventually reach an arrangement that we would call "us." At some point during or after death, those molecules undergo physical and chemical changes until they become unrecognizable as "us;" personally, I would consider brain death to be the marker for when "we" stop existing.
I also do not agree that there is a God or that we have free will, so I cannot affirm the second part of your statement, either. I think we are the product of deterministic natural forces which have certain mathematical patterns to them, but are nonetheless mindless.
I think what we call a "mind" is merely an abstraction of a certain kind of computational system, the most well-known example being the neural activity of our brains. We call the output of this computational process a "choice," but that choice was always fated to be made. There was never any ability for us to have "chosen differently" or a future where we did not make that choice.
As far as I can tell, our choices are simply a product of how our genetic predispositions are conditioned by our environment, so they are always fixed. The deliberation that we make before we decide upon something is, itself, a linear process of cascading effects from causes that we have no direct control over. It gives us an illusion of agency only due to our limited cognition, since we cannot fully comprehend the multitude of processes that our nervous system undergoes which generate mental activity, but we have become increasingly aware of this through study and experimentation.
Furthermore, as far as I'm concerned, "sin" is a concept that other people use. I can describe what is considered sinful according to certain philosophies and scriptural interpretations, but I'm not sure that I would confidently assert that anything is a sin, myself. As such, I don't think I would consider departure from God to be a sin. If I was to use the language of "sin" at all, I would reserve it for describing vice and passion, and I do not see anything vicious or passionate about self-generation by itself.
There may have been a vicious or passionate reason for self-generation, in which case I might be able to agree that doing so would be sinful, but you haven't really gone into detail on that. Speaking for myself, I have never been one with God and I never chose to separate myself from that oneness, so I have no frame of reference for why you might have chosen to do something like that. Maybe some people who chose to separate had good reasons for doing so, how would I know?
