In the discussion under Intelligent Design and Evolution, Kirby and Olorin have been going back on forth on the relation between science and ethics.
The proof of the pudding of the sort of pluralism I've inherited and which I'm developing here and elsewhere is in the eating, esp. when it comes to these sorts of issues. Here, I want to contrast pluralism with two bad alternatives.
The first option, and which is in many respects the dominant discourse of academic philosophy and the academy generally, is a version of "scientism." This much-abused term will stand in, here, for the notion that scientific methods are the only legitimate processes whereby objective knowledge (which goes beyond ordinary perceptual consciousness) can be acquired. (I'm not delighted with this definition and may need to revise it subsequently.) On this view, "values" pose a number of interrelated problems. One problem is that when scientific theories are taken as having a monopoly on objective knowledge, values may become seen as "subjective." Apart from the considerable ethical and political problems this causes, it also arouses the philosophical problem of how to fit "values" into a world of "facts." In this case, the relation between science and ethics can be seen as arbitrary, science can be regarded as "value-neutral," and countless other difficulties arise like the heads of the Hydra.
The second option, which stands in a dialectical relation to the first, is to give ethics a metaphysical foundation (see note (1) below). On this view -- which, I must admit, I lack any real intuitive feeling for -- values cannot be merely subjective or conventional, but they also cannot be grounded in the sort of knowledge that science yields (but see note (2) below). Thus values cannot be "natural" but must instead have some sort of transcendent foundation. Alternatively: when the very idea of a transcendent foundation ceases to be rationally compelling and emotionally motivating -- i.e. the moment of "the death of God" -- then the abyss of nihilism threatens to yank out the foundation of civilization from under our very feet. There is something tiring and boring about how this argument then proceeds -- as if on cue, the exhibits are presented -- Exhibit 1: Nazism; Exhibit 2: Stalinism; Exhibit 3: terrorism.
The alternative I wish to explore takes its cue from a remark by John Dewey: "But values are as unstable as the forms of clouds" (Experience and Nature, excerpts available as PDF here). The forms of clouds! Are they not real? To what sort of reductive, scientistic physicalism must one be beholden in order to insist that clouds are not real (are not "really real")? If clouds are not real, I want to say, then nothing can count as "real". And so too are values -- they are as real as anything other aspect of our lived experience as a certain kind of animal -- the sort of animal that engages with its world through a plurality of discursive social practices.
(1) The dialectic, as I see it, can be seen roughly as if each viewpoint is a reaction-formation to the other. Thus, the Greek atomists reacted against ancient Greek religion and made possible the Sophists; Plato and Aristotle reacted against the Sophists; early modern philosophers reacted against Scholasticism; the Romantics reacted against the Enlightenment; religious fundamentalists reacted against 'modernity'. The "culture wars" have been with us for a long, long time!)
(2) Off the top of my head, I can think of two exceptions in the history of philosophy -- Aristotle and Spinoza -- who hold that ethics is grounded in the metaphysical structure of reality and that science provides insight into this structure. But Aristotle is a tricky case, since "science" does not mean for us post-Baconians what it mean to Aristotle or the Scholastics.