You want more good and less bad in the world? Would it be better if we had a little more good and a little less bad? If so, then we should care about the efficiency of our efforts to make the world better.
*note that I of course here mean something like efficiency that includes Pareto efficiency, not the narrow notion of efficiency we use everyday; you could also say “effective” but you asked for why giving should be effective, and we can ground effectiveness in Pareto efficiency across all dimensions we care about
You want more good and less bad in the world? Would it be better if we had a little more good and a little less bad? If so, then we should care about the efficiency of our efforts to make the world better.
*note that I of course here mean something like efficiency that includes Pareto efficiency, not the narrow notion of efficiency we use everyday; you could also say “effective” but you asked for why giving should be effective, and we can ground effectiveness in Pareto efficiency across all dimensions we care about