The switch flipped for me when I was reading Jim Holt's "Why Does The World Exist?" and spent a while envisioning and working out the implications of Vilenkin's proposal that the universe may have started from a spherical volume of zero radius, zero mass, zero energy, zero any other property that might distinguish it from nothingness. It made clear to me that one could propose answers to the question "Why is there something rather than nothing?" without anything remotely like a deity.