Well, since this thread has completely gone off topic and is now discussing a much broader and hazier issue (as internet threads are wont to do... err, that might be ascribing a "will" to a thread, but whatever...)

...I'm not going to try to get it back on topic and will go along with the current discussion.

I don't see how anyone can argue that morality is purely subjective. I would think it should be quite clear that there are some propensities to certain types of social behaviors that could be called moral behaviors, though just as anything else their expression is regulated by culture.

I think strong evidence for this can be seen in our mammalian cousins, especially those that function in social groups. Their is obviously some social code that governs their behavior which may be considered sort of proto-morality. If their expressions of social norms and of principles that govern their social interactions are not cultural (at least not purely), then humans should probably be no different.

Going along with this, a somewhat old model of the evolution of human social behavior is gaining popularity again amongst evolutionary anthropologists. I can't quite remember the name it goes by, but it's thought that groups of humans were competing with each other for resources, and those groups with individuals were disposed to cooperative social behavior won out against those groups which were not. In addition, these cooperative groups tended to reject and kick out individuals that did not have a disposition to cooperation, which caused the favoring of genes that encouraged cooperative behavior to be passed on.

Thus, this model could explain why humans seem to be predisposed to certain basic of moral behaviors, such as simply not killing every person they lay eyes on for fun. Again, however, there is merely an average tendency for this behavior over an entire population, and culture can greatly alter behavior. Just as with most other human behavioral characteristics, there is a complex interaction between genes, culture and environment that ultimately determines expression; it is not simply "nature" or "nurture."