DP: Meta, you have studied the history of science so what I'm about to type really shouldn't need to be pointed out to you by a novice like myself. However ....

There are currently two theories which explain different aspects of reality which are General Relativity (large phenomena) and Quantum Mechanics (miniscule phenomena). These theories are known to contradict each other which is why the search is on for a unified theory of everything.

How could a set of contradictory and partial laws be considered prescriptive? The reason why any atheist with a basic knowledge of scientific history will argue that scientific laws must be viewed as descriptive rather than prescriptive is because they are aware of the above problem. We know that our current description of reality is contradictory and incomplete and thus, needs improvement.