Consider what is at stake in taking on subjectivism as Parfit has done. Mathewes, in his book, Evil and the Augustinian Tradition writes:
"Insofar as our thought remains in the thrall of subjectivism, we cannot adequately respond to evil's challenge to us, and any subjectivist response to evil's challenge will be vexed by the challenge's complexity; we either take it too seriously, and think of evil as a natural reality; or we do not take it seriously enough, and assume that, since it is due to us, we can straightforwardly change our actions and simply overcome it. That is, modern thought cannot handle evil because of its essentially subjectivist tenor..."Subjectivism" here means an account of human existence which gives priority to the human intellect, and/or the brute fact of human action, over against some mute and inert reality, material or otherwise."(pg. 52)
It seems in this passage that Mathewes is assuming that we agree that certain things are evil, rather than starting with raw nihilism. What he says is that moderns either resign ourselves to evil as just part of nature and thus unavoidable, or we buy into notions of human progress... He then clarifies what he means by subjectivism itself. The human intellect ovder against the inert material world. The material world has no moral order(think Discovery Channel here) ;we are left construing morality as resting in subjectivity. This is one of the reasons, at least, why Mathewes can say relativism is a 'local manifestation' of this subjectivism.
Now, I know that Parfit did a lot of thinking about human identity that I haven't read and maybe there is some depth to his thought here that bears upon his attempt to defend a normative ethics; here I confess my ignorance. But, from what I read, NOTHING he wrote successfully defends normative ethics. Absolutely NOTHING. I am still left with nihilism. PERIOD.
Mathewes writing is actually more probative to me. He writes plainly that the problem is subjectivism, that relativism is one of its offspring. The implication is that we have to undercut this subjectivism. Now, ultimately, Mathewes is coming from a theological position, which has its own problems, but ultimately seems more understandable than attempting to make something out of nothing as Parfit attempts.
I might as well come clean and tell you my commitments. I am an atheist materialist. I think freewill is an incoherent notion. I think things that cause purposeless suffering to others are bad but I don't think this claim is anything other than my own response to it-- it has no logical defense whatsoever. Does this make me a nihilist?