We know that such a model or standard exists because we trust that God did not create some sort of silly and simple-minded game for humans to take part in.
Why is this nonsense?
Maybe because we don't
know that any gods exist. If any do, we don't
know that they don't absolutely delight in making folks play silly games. Maybe because "perfectly right and good" has no meaning out here in the world, but only as a simplistic mental construct.
The choice between right and wrong has always been subjective, Prophex: it's determined by the culture one lives in. Actions that we 21st-century Americans say are deeply immoral have been perfectly moral at other times and in other places. Take slavery or the death penalty for ten-year-old pickpockets.....