What is the nature of ethics anyway? Is it something that we discover about the world or is it something that we attribute to the world? Before we can answer this question, we must understand it, so what does it even mean to label anything as subjective or objective?
- Let's take a spoon, for example. Its shape depends only on itself and not on any subject that perceives it. This is because what we're calling shape is only a function of how the spoon's molecules are arranged in space and, as far as we know, their arrangement doesn't change depending on who's perceiving it. Hence shape is a property of the object and is therefore objective.
- As for a subjective perception, we could use beauty as an obvious example. Beauty is a property that does not seem to resides in the object itself, it seems to be only a feeling, the result of the experience of perceiving the shape and/or colors of an object. We could also use the less obvious but easier example of color. It's less obvious because each color correlate with an objective feature of the world (namely, the wavelength of the photons that reach our eyes) but the experience of redness is subjective because it doesn't follow from the photons themselves, it's only a mapping in our minds between the wavelength of the photon and the actual experience of color that surfaces into consciousness.
- The usual arguments that I see being used are arguments of the type: "Western moral standards are different than eastern moral standards, which is just one example that proves the subjective nature of morality" or "Don't you think that at least some things, like murder and rape, are truly wrong regardless of the time and place?". This is the most common obstacle that is usually stumbled upon, it's this misunderstanding that an answer can be found by observing moral variability in the world.
Let's go back to the spoon example. We can all disagree about its actual shape (due to perspective/optical illusion/faulty vision or any other cause) and that wouldn't automatically mean that its shape is actually a subjective property that we're attributing to the spoon. Because of what we know about the world, we know that shape depends on the object, not the subject, even when different subjects see different shapes. So variability doesn't entail subjectivity, but can the lack of variability entail objectivity? Let's imagine that suddenly, all people that dislike the taste of chocolate die. Everyone would find chocolate delicious but that would do nothing to establish the nature of that property as being dependent on the object. Also, we can all agree that the sunrise is beautiful and that doesn't necessarily mean that the sunrise is intrinsically beautiful, independently from the subject that experiences it. "Beauty is in the eye of the beholder", right?
So, as you can see, observing the amount of variability of one thing isn't very useful in finding its nature. I believe that the question can't be answered by observing the thing we're testing alone, in isolation from its context, it's in examining how it fits within our world-view that we can find an answer.
Now you're probably wondering how can we possibly answer such a question after I claimed that the answer will come ultimately from what your world-view allows and how morality fits in it. It's probably impossible to arrive at an answer without a prior agreement on an underlying world-view but I believe we can reach a conclusion for a naturalist world-view at least. Part 2 will be up shortly, I'll edit this paragraph to point to it but for now, I hope I've been able to clarify what the question means and to make sense of it.