Measuring Social Impact vs. Private Market Profit Margins

While I don't think I agree with what Geoff Mulgan writes about measuring social impact, or at least the main thrust which is that value is mostly subjective, I do like the fact that he pointed out that social ventures would benefit from the private market approach of using different metrics to determine where to invest resources, return on investment, etc. In other words, there isn't any one single number that you can just throw out there that will make a venture or project worth doing- instead you should be able to find out how much people will value it (demand curve), what costs are acceptable to you as a firm with your own specific company culture and needs (supply curve), what the probability of success is, and so forth. I think Mulgan is mistaken, however, when he claims that assigning an objective dollar value to any of these metrics and instead assigning a 0-5 subjective score, is the best route. This brings me to my main point which gets to the nature of the development industry. If my venture were to use subjective assessments of a project's value to consumers and to the venture, it would most certainly be undercut by industry trends that promote high perceived value at low cost. That is to say that in development, a value-added product like a green home isn't necessarily valued by society unless its true value is made explicit. I use the example of big box retail a lot, but the reason the big box model has been so attractive to the development community is because it offers consumers huge monetary value for relatively little money (think Sam's Club). Developers achieve the same high rewards for minimal input, and they always have in mind a profit margin before even starting a project. One of their first acts is to project, using market research, traffic studies, etc. how many people will use a building and how much they will value its service. What good would it be for me, a green developer, to use a 0-5 scale to measure my venture's potential benefit for consumers? That would be like saying to a potential renter who is looking at other offerings around the city, "yes sir, our apartments are more expensive, but they're worth a 4 out of 5 in energy savings." The very nature of a value-added service like ours has a pretty real dollar value attached to it because it is designed to save consumers $x over the long run. And as for the uncertainty, sentimentality, or biases of consumers weighing on their opinions, I believe that market research, statistical trend analysis, forecasting, etc. are enough to predict product or service value fairly accurately.