"I think you could even narrow it down to the belief (in the religious sense of the word) that technology collectively isn't subject to the law of diminishing returns."

I don't know any serious "singularitarian" who believes that. Maybe this belief is common amongst poorly informed fanboys, but I haven't seen any evidence of that either. (BTW, I know quite a few singularitarians.)

Or that intelligence has untapped economies of scale. The Singularity doesn't usually call for indefinite growth, just growth so rapid that it makes predictions meaningless.