I'm probably gonna get downvotes for appearing to bask in this attention (which I didn't expect).

In this case it's based on a heuristic. I can't at all model human will so it seems reasonable to start with it as infinite (since it's so vast and appears virtually limitless, the very reason I can't model it in the first place) and model in the constraints.

edit: also, I am a Christian and that probably factors into my view subconsciously, although I am certain many non-Christian views would arrive to the same conclusion.