I agree that the words "objective" and "subjective" serve more to confuse this issue than to clear it up. I thought at first "oh, clearly subjective" until I read some more posts and thought about it a little more...what do I mean when I say subjective? So here's my reasoning, trying not to use the terms "objective" and "subjective." (Bear in mind that I'm reasoning as I go, and that I have not read the other threads on the same subject, so I might not be on the same track y'all are on.)
It is clear that what is considered ethical/moral behavior has changed over the course of human history.
Does that mean that our morality as a species has changed?
I see a few different possibilities.
1. Our morality comes from an outside sourse, a "god" of some stripe, that has itself changed its ideas about what constitutes moral behavior. (This might be considered "objective" if by objective you mean "outside the human mind," although you're still left with the question as to whether morality is subjective to the "god" that imposed it upon us.) I find this idea neither plausible nor useful, but I'm including it because it is a possibility.
2. Our basic code of morality, something along the lines of "it is unacceptable to take certain actions against certain individuals," has been hardwired into us over the course of our evolution as a species, and any changes we see in what is considered "moral behavior" are not changes to that basic code of morality, but instead reflect changing attitudes as to the scope of the code. In other words, the code stays the same, but we change our definition of "certain actions" and "certain individuals." For instance, the parameters could once have been: "It is unacceptable to kill a male member of one's own tribe. (Obviously, this is an oversimplification that ignores things like deviance from the accepted social order. I think the basic premise still holds even if you make the "code" in question more complex.) Over time, the parameters have changed to something more like "It is unacceptable to knowingly cause pain without consent to any member of the human species, and maybe some animals, if they're cute and not tasty." (If the basic code remains the same, and we just change parameters as society changes, then one could argue that "morality", but not "moral behavior" is objective, if by objective we mean "hardwired by evolution.")
3. The "moral code" I just posited is too vague to be workable as an actual moral code, and our "morality" is in fact nothing more or less than the general consensus of a particular society regarding "moral behavior." Thus it changes from place to place and over time, and is in fact subjective, but seems objective if only one society's norms are considered, since the vast majority members of that society subscribe to the same norms.
In scenarios 2 and 3, there will always be people who do not believe in their own society's current standards for the parameters of moral behavior, but most of these will fall into line because of societal pressure/punishment. In scenario one I suppose such people would be...aberrations? broken? evidence against scenario one?
anyhow, there's my reasoning. I think I'm leaning towards scenario 2, but I'm still not sure if that would be considered "objective" or not.