Somebody: Even apes have a sense of fairness. That in itself is good reason to believe there's probably an innate element contributing to human morality. I don't get how *materialists* can focus only on social influences to the exclusion of our corporeal bodies. Either way, it's a matter of empirical study, not exegesis of mid 19th century texts. We can't just always put a minus where Steven Pink puts a plus, because he's a reactionary douche bag.
Anyway, there's two separate issues here. The second issue is whether there's a notion of justice beyond the contingent frame of reference of our "social lives" which in Marxist jargon just means in terms of how we're going to win the class struggle (how many kulaks we're allowed to kill; answer: as many as it takes), or whether there should be a trans-historical notion of justice. I vote for the latter. It doesn't have to be based on appeals to anything mystical, we can just all sit down in a *social* context, if you will, and agree upon some moral rubric.