How about looking at the feasible region in "cost/benefit space" and finding the efficient boundary where it is impossible to increase the benefit without also increasing the cost? The mathematical analisys ends there, with a collection of multiple pareto-optimal solutions, and then it becomes a political decision to choose a single solution as a goal.

Anything else is trying to abdicate to mathematics our responsibility to make our own decisions.

"It's the statue, man, The Statue."