Cultural relativism is one of those things where I nod in agreement for the first 9/10ths of a given sentence, but then wonder what happened when it concludes with, "Therefore, it was perfectly acceptable for Culture X to practice slavery/cannibalism/infanticide/systematic rape/whatever, because they considered it to be morally right."
Helgoland's put forward a much better variation, judging individuals not as if the standards of their culture were all hunky-dory simply because they thought they were, but in terms of how they acted within those societal constraints. That's what he was getting at, PoH. Yes, I'd not hesitate to assert that ritualistic murder is objectively wrong -- I don't subscribe to the central argument of cultural relativism, and think that killing a person without meaningful justification (that is to say, not in legitimate self-defense &c.) is not acceptable. However, there is a difference between an individual of that society who deliberately makes victims suffer and one who kills their sacrifices painlessly; both are operating within the moral and ethical framework of their society, but the latter is a "good" person insofar as that their offenses are those dictated by societal norms rather than personal failings or depravity.
It's not reasonable to judge individuals wholly by the standards of a culture or society not their own, but neither is it reasonable to judge them only by the standards of their own. At least not if you're interested in an honest examination of the moral and ethical status of their actions, rather than passing judgment with sweeping generalizations.