Of course, it isn't that simple.
Although firms and their shareholders are the principal beneficiaries, the public also gains: employment and the expenditure of associated salaries and wages; the production of goods that people need or want; and further investment by shareholders.
Sometimes, the argument goes, these broader benefits outweigh the associated societal costs. Forcing producers to internalise all their costs could see some of them withdraw from the market or fail because their products are too costly. And that is where the arguments begin.
Who should pay what? Who benefits and who loses, in what ways, and by how much? How do you measure it all?
There is a flip side to this idea.
It involves the case where others benefit substantially from the actions of individuals or firms working in their own best interests. The most commonly cited examples are in the fields of education and healthcare. For example, individuals who pay for their higher education eventually benefit us all by becoming better skilled and more economically productive.
This is what economists call a 'positive externality' (as opposed to the 'negative externalities' discussed above): a benefit that is enjoyed by third-parties as a result of an action in which they are not directly involved.
We surely have an interest in promoting positive externalities.
So let's consider conservation. Some people work to maintain environmental quality or recover a degraded resource or ensure that we continue to benefit from the services that we get for free from properly functioning ecosystems: clean water; fresh air; productive soils; pollination; pest control.
Controlling erosion, protecting waterways and catchments, conserving biodiversity, and maintaining ecosystems, all produce positive externalities.
If we penalise those who create negative externalities, by applying PPP, shouldn't we be equally willing to support and reward those who produce positive externalities, to encourage them to continue doing so or do more?
After all, there are usually both direct and opportunity costs to their activities, which currently they bear privately, while we all benefit.
Aargh! a "subsidy", I hear you scream. But is it? Isn't it just sensible to reward those whose activities benefit society more broadly?
To me, accommodating a negative externality sounds like the real subsidy.
Paying to maintain environmental services is perhaps an idea whose time has come. It has elsewhere in the world. Why not here?
-Peter Frost is an environmental scientist who has worked on issues of environment and development overseas. He wonders if our current approach to environmental issues is sufficiently holistic.