Many conservationists have become enamoured with mainstream economic concepts and approaches, described as pragmatic replacements for appeals to ethics and direct regulation. Trading biodiversity using offsets is rapidly becoming part of the resulting push for market governance that is promoted as a more efficient means of Nature conservation. In critically evaluating this position I argue that offsets, along with biodiversity and ecosystem valuation, use economic logic to legitimise, rather than prevent, ongoing habitat destruction. Biodiversity offsets provide a means of commodifying habitat for exchange. They operationalise trade-offs that are in the best interests of developers and make false claims to adding productive new economic activity. Contrary to the argument that economic logic frees conservation from ethics, I expose the ethical premises required for economists to justify public policy support for offsets. Finally, various issues in offset design are raised and placed in the context of a political struggle over the meaning of Nature. The overall message is that, if conservationists continue down the path of conceptualising the world as in mainstream economics they will be forced from one compromise to another, ultimately losing their ability to conserve or protect anything. They will also be abandoning the rich and meaningful human relationships with Nature that have been their raison d'être.