I consider that human beings are capable of some independence of thought, but that we will always be very much the product of the sum of our experiences -- and in terms of the shaping of our general character, most especially the sum of our early experiences. The person who was taught as a young child to fear God's punishment will be very, very hard-pressed to reject that idea as an adult. This much is clear to anyone. The things are are most deeply impressed with during our earliest, formative years will forever be a part of our thought, no matter how hard we try to be completely independent and objective.
I grew up a very badly battered child, deeply scarred but with no god-belief that I have ever been aware of. As a result of my abuse, my principle values are humanistic and liberal, seeking fairness and decency for all people, and despising injustice. I cannot help that, and I cannot change. My perspective will always be skewed by totality of my experience. (Of course, I don't want to change it, either. My humanist viewpoints seem most natural and good to me.)
So, no, I did not arrive at my conclusion about no deity through reasoning -- I never believed it at all. But reasoning, now that I am capable of it, tells me that it is the right conclusion, because I do not have that nagging early indoctrination to cause me to reject my reasoning.