Problems arise when a situation invokes moral principles that are themselves in conflict and no single proper course of action can be deduced. Faced with disagreement about the moral principles that should guide our actions, Kant did not theorize at length about situations where principles compete. It is fair to suppose that the proper course might be to undertake a process of public deliberation leading to the enactment of legislation within constitutional constraints. By legislating and following moral rules, we determine our moral character and identity as a nation.
We are now in a position to understand the difference between utilitarian and Kantian theories of value. For utilitarians, society has no moral identity independent of the welfare of its members, who judge what benefits them. All values but welfare are instrumental or subjective. Ideally, everything but welfare itself can be assigned a value that indicates its relative worth with respect to promoting well-being. For Kantians, in contrast, value attaches to outcomes that reflect the rules or duties that we as a society accept as appropriate given our evolving identity and our understanding of the situation. Whereas utilitarians are comfortable with a scheme that values the practical and the aesthetic, and the public and the private, on the same scale, Kantians are at pains to confine relative valuation to the practical end of the continuum. Kant draws this distinction as follows: "That which is related to general human inclination and needs has a market price. But that which can be an end in itself does not have mere relative worth, that is, a price, but an intrinsic worth, that is, a dignity." Kantian ethics, however, have not resolved the problem of deciding what to do when "ends in themselves", that is, those things too important to trade off, conflict.
Kantian ethics appeals directly to the concern that preferences alone are an insufficient guide right action. In the Kantian system, aesthetic judgment, intrinsic values, and moral principle can and should trump preferences in a considerable variety of circumstances. However, several problems arise in the Kantian system. It is not clear which things have "a good of their own" independent of contribution to human welfare.
John Rawls proposed the egalitarian criterion that inequality should be tolerated only insofar as it improves the well-being of the worst-off individual. The general problem with Rawlsian egalitarianism is that its exclusive focus on the worst-off might undermine incentives and freedom of action for everyone else. Implications of this kind of egalitarianism for environmental quality and biodiversity are unclear. If, as some suspect, environmental improvements have lower priority for the worst-off people than for the well-off, an egalitarian approach might lead to reduced provision of environmental public goods.
Environmental justice focuses directly on environmental quality for the worst-off people. The basis concern is that public policy not worsen the situation