> Let me try again: why are we compelled to "give the avoidance of
> needless suffering any non-negligible ethical weight"? It's possible
> and quite common that avoidance of suffering is not a component of
> moral decisions and action.
Since you seem to be more interested in moral anthropology than moral argument, I'll note that there's no evidence at all that it's "quite common" for ethical systems to take no interest in what harms we're obligated to avoid inflicting and what benefits we're responsible for doling out.
> I suspect you'll hate my answer, but I'll state it anyway: if the
> social consensus among humans was that the aliens are human-like,
> and deserve respect, then it would not be okay. If the consensus
> was that the aliens are a danger, or a source of food necessary to
> keep people alive, then--in that social world--it would be okay.
It's a position that devours itself. One of the more robust areas of social concensus on moral matters is as follows: the truth values of ethical claims aren't entirely contingent on social concensus. You'd have a very hard time convincing anyone (other than perhaps a few renegade pomos) that enslaving the blacks was OK back when most Americans were comfortable with it.
Perhaps Justin could say something interesting about Rorty's notion of liberal irony, which from my reading of secondhand accounts seems to amount to the following: as an intellectual matter, we're forced to acknowledge that our ethical/political ideals are utterly contingent and perhaps as an empirical matter not widely shared, but that as a practical matter we ought to seek their realization anyway.
> To steal shamelessly from Wittgenstein: moral claims are part of a form of
life; they are not fundamental axioms that exist above
> and beyond the social relations that create them.
That sounds a hell of a lot more like Marx than Wittgenstein. The latter was an emotivist; not a subjectivist. As an error theorist, I'm a bit skeptical of the distinction, but Wittgenstein probably wasn't.
-- Luke