A colleague said to me,

I have my own personal doubts about contingent valuation when respondents are ethically committed to environmental preservation. If they are asked a willingness-to-accept question, then they may respond with an infinite or very large price. In essence, they see the resource as priceless or incommensurable with respect to monetary values. If they are asked a willingness-to-pay question, they may object on grounds that they are being forced to pay for something that has ethical standing and on moral grounds should not be damaged or destroyed; or they might simply offer what they can afford in order to meet what they see as their moral obligation to save the environment. The point is that contingent valuation analysis, while interesting, could be conceptually problematic.
Do you agree or disagree with my colleague? Why, or why not?