@browncoat - It does help to put a financial cost on many social costs though. I've seen analyses that attempt to put a price tag on the benefits of wetlands, for example, in the way they filter water and provide other ecosystem services (like preventing floods) that would have to be replaced if they disappeared.
Maybe people should be able to stop doing bad things just because they know it will hurt the world, but the world isn't that simple. It's very difficult to determined whether it's better to drain the land and plant crops that can feed hungry people, or keep it as a wetland with all that implies, without being able to compare the two scenarios on equal grounds.
Money is quantifiable and people understand it in general terms. They might not understand about flooding cycles, but if you tell them that the cost of getting that farm is going to be millions of dollars in flood wreckage every year, they will definitely understand that.