Why do Athiests require 'proof' that God exists?

[Neo-Scholastic]

...every domino would be connected to another domino in another pattern. Thus, consciousness would not be an epiphenomenon, it would be a function that connects the stimulus to the response.

I don't see where consciousness gets inserted into the causal chain. Suppose the brain in question was not organic, but a series of gears, levers and hydronic pumps. The interactions of those parts would be clearly visible and seen to act one upon the other to produce behaviors normally associated with consciousness. But you wouldn't see anything related to sensation or experience involved.