Sagoff, M. (2008). "On the Economic Value of Ecosystem Services." Environmental Values 17: 239-257. L:\Public\EcosystemServicesReadings\Sagoff 2008 On the Economic Value of Ecosystem Services.pdf.

• In this essay honouring Alan Holland, I shall argue that markets already assign efficient or competitive prices to goods ecological economists identify as ʻnatural capitalʼ or as ʻecosystem servicesʼ, even if these goods are ʻtoo cheap to meterʼ and thus even if the price is often zero. I agree with Holland that moral, aesthetic, cultural and spiritual arguments are enough; they provide compelling reasons to preserve the magnificent aspects of the natural world. I question whether there is any ecosystem product or service which does not already receive a more or less objective market price – and thus which should be given a ʻshadowʼ or imputed price in our spread sheets and in our cost-benefit analyses.
• I think on the contrary that nature has no economic value. The reason is not that nature does not benefit us in every way – of course it does – but that nothing has economic value. The phrase ʻeconomic valueʼ has no coherent reference.
  Economists from Locke to Marx thought the term referred to the input of labour, but it is hard to find anyone who propounds this view seriously today. Ecological economists use the term to refer to a construct, such as ʻemergyʼ, ʻlow entropy resource flowsʼ, or something of that sort I do not presume to understand.
  Welfare economists equate ʻeconomic valueʼ with WTP but no one has ever shown empirically a correlation between WTP and any conception of the good – e.g., ʻwelfareʼ, ʻbenefitʼ or ʻwell-offnessʼ – not trivially and vacuously defined in terms of it. No one has measured use value, benefit or utility, for example,
  to test whether or not it varies with embodied labour, embedded energy or willingness to pay. Economists simply use terms like ʻutilityʼ or ʻbenefitʼ as logical proxies, stand-ins or equivalents for whatever they think is the source of value. The term ʻeconomic valueʼ may be defined in whatever way one likes – some like to define it in terms of WTP, others in terms of energy flows, and still others in terms of labour – but it has no testable, defensible, non-circular normative meaning or content.
• To be sure, the amount someone is willing to pay for something correlates with its ʻutilityʼ if ʻutilityʼ is measured in terms of the amount he or she is willing to pay for it. There is no way beyond this tautology get from WTP to value from a social point of view.
• To defend the ʻmarginalʼ value of biodiversity on economic grounds is to trade convincing spiritual, aesthetic and ethical arguments for bogus, pretextual and disingenuous economic ones.
• The attempt by economists to ʻvalueʼ by ʻpricingʼ ecosystem services only creates confusion because price does not correlate with value, benefit or utility. By ʻputting a price on itʼ we abandon the rhetoric of reverence; we regard nature as a resource to exploit rather than a heritage and an endowment to maintain. This is the most self-defeating path environmentalists can take.
• Everyone agrees, of course, with platitudes about how plentifully and freely nature sustains us, comforts us and inspires us. We recognise that the preservation
  of the beauty, complexity and integrity of the natural world represents an aesthetic opportunity, a spiritual duty, and a moral obligation. Alan Holland is correct in his critique of the attempt to reckon the ʻvalueʼ of environmental goods in pounds or pence. The prices at which goods trade hands may reflect their scarcity relative to demand or their cost to produce but not their ʻvalueʼ in any sense – neither the ʻmarginalʼ benefit they provide nor the intrinsic worth they possess nor the reasons they are important. That is why the best things in life are and ought to be free.