I think that “morality” is a product of human thought which does not actually have any objective reality outside of human thought. Essentially, I believe that groups of humans, on a micro level and a macro level, have attempted to formulate a consensus for behaviors which basically fall into three broad categories: desirable (or “good” or “right”), acceptable (morally neutral), and unacceptable (or “bad” or “wrong”). Oftentimes, these codes of behavior have been mystified, or perceived as having been derived from a more divine authority.
Generally the consensus about what behaviors should be expressly forbidden is what has been most important to people.
Usually these are behaviors which cause obvious and gratuitous harm to others. Murder, rape, theft, assault and the like are generally recognized as undesirable behaviors in any human society.
Most political and philosophical conflict over morality springs from the wide variety of behaviors which have often been deemed undesirable or “immoral” by various cultures, subcultures and religions which do NOT cause any obvious harm to others. Archaic beliefs about ritual purity once led to proscriptions against homosexuality and having contact with menstruating women. A once genuine concern about simple health led to strict dietary codes. Other taboos were derived purely from a superstitious fear of angering gods. (atheism, working on the sabbath, worshipping idols).
Much “morality” is amorphous, ambiguous, ever-changing. As human understsnding of the world changes, so does human consensus about behavior. We no longer fear divine reprisals for idol worship or marrying “foreign” women. We no longer accept any notions of racial superiority/inferiority, and have changed our codes accordingly.
Other behaviors, though, are still clearly harmful. The consensus has not changed about *murder, rape, robbery and assault. If anything, consensus has widened to offer MORE protection from these behaviors. So in that sense, I would say that there are at least some behaviors which have a virtually universal consensus for being defined as “absolutely” immoral. This is probably the closest thing we can get to an “absolute” moral value without resorting to the supernatural.
*Ironic point: it is interesting, is it not, that the one behavior which humans find the most undesirable, the taking of human life, seems to be the one “absolute” taboo with the most loopholes and exceptions.