Could you please describe to me the differences between a moral system that exists (in the same sense of the verb "to exist" that you used in this post) and a moral system that does not exist?
I have edited my post in such a way that the terms are now more clear.
If moral system is a normative theory, then there are many.
If moral system is morality, then there is only one.
If you blur the details enough, you can make it look like everyone agrees. That doesn't mean they really do. For example, the UN's Universal Declaration of Human Rights is something that almost every human agrees is good; but suppose you take two different rights from it, and have to make a tradeoff between them. For example, take number 4, which prohibits slavery, and 5, which prohibits torture. You have some resources to spend, and you can either free X slaves or prevent Y instances of torture. What is the ratio of X to Y that makes freeing slaves more worthwhile than preventing torture? You aren't going to get near-universal agreement on that question, even to within an order of magnitude.
And it's not just a matter of quibbling details, because the agreement we do have comes from culture and some innate characteristics of humans, which aliens would not necessarily share. The wider the variety of viewpoints you include, the more details you have to blur out. If you include aliens in general, then there will be very little in common. And if you include Clippy, then there will be nothing in common whatsoever.
1) The fact that we do not have a near-universal agreement now does not mean that we won't have one in future. It also does not mean that there is no one correct answer.
2) What you are saying is that currently we are not very precise, or not as precise as natural science. That doesn't mean that we are not going to be closer to the correct answer in the future.
3a) Analogously, if we compare different viewpoints about the natural world and looks for the common, then there is also very little we can agree on. Maybe only on a few parameters like colour, form and number. Or even less.
3b) What if there are lifeforms that exist (are evolutionary successful) without any concepts of mathematics and visual perception? What if they have nothing in common wahtsoever with us? Is our physical reality also just as "relative" as our morality?
4) There are differences between the natural world and the normative world. I am certainly not implying that the normative world has the same qualities as the natural world and that you can explore the normative world in the same way as you explore the natural world. So please understand my references to natural science as vague analogies only.
5) You can read my post as a defence for an absolute morality or as an attack against an absolute physical reality. I feel that people on this website are easily ready to attack the notion of an absolute morality, while taking an absolute physical reality as self-evident.
6) Maybe neither the natural world nor the normative world is absolute and as total sceptics, we all become solipsist. But in our everyday life, when we are too busy with the details of life to be sceptic, we subconsciously assume the natural world to be real. In the same way, we can handle the normative world "as if" real, just because its useful and fun.
The following is destilled from the comment section of an earlier post.
Definitions
absolute and universal: Something that applies to everything and every mind.
morality (moral world): A logically consistent system of normative theories.
reality (natural world): A logically consistent system of scientific (natural) theories.
normative theory: (Almost) any English sentence in imperative or including the word "should", "must", "to be allowed to" as the verb or equivalent construction, in contrast to descriptive theories.
mind: A mind is an intelligence that has values, desires and dislikes.
moral perception: Analogous to the sensory perceptions, a moral perception is the feeling of right and wrong.
Assumptions
A normative sentence arises as a result of the mind processing its values, desires and dislikes.
Ideas exist independently from the mind. Numbers don't stop to exist just because HAL dies.
Statement
In our everyday life, we don't question the reality, due to our sensory perception. We have moral perception as much as we have a sensory perception, therefore why should we question morality?
If you believe that the natural world is absolute and universal, then there is -- I currently think -- no good reason to doubt the existence of an absolute and universal moral world.
A text diagram for illustration
| sensory perception | ----------------------- ------------
| + | -- | scientific theories | -- | reality |
| intersubjective consensus | ----------------------- ------------
-----------------------------
Analogously,
-----------------------------
| moral perception | ----------------------- ------------
| + | -- | moral theories | -- | morality |
| intersubjective consensus | ----------------------- ------------
-----------------------------
Absolute moralily
The absolute moral world, I am talking about, does encompass everything, including AI and alien intelligence. It does not mean that alien intelligence will behave similarly to us. Different moral problems require different solutions, as much as different objects behave differently according to the same physical theories. Objects in vacuum behave differently than in the atmosphere. Water behaves differently than ice, but they are all governed by the same physics, so I assume.
An Edo-ero samurai and a Wall Street banker may behave perfectly moral even if they act differently to the same problem due to the social environment. Maybe it is perfectly moral for AIs to kill and annihilate all humans, as much as it is perfectly possible that 218 of Russell's teapots are revolving around Gliese 581 g.
The intersubjective consensus
There are different sets of theories regarding the natural world: the biblical view, the theories underlying TCM, the theories underlying homeopathy, the theories underlying chiropractise and the scientific view. Many of them contradict each other. The scientific view is well-established because there is an intersubjective consensus on the usefulness of the methodology.
The methods used in moral discussions are by far not so rigidly defined as in science; it's called civil discourse. The arguments must be logical consistent and the outcomes and conclusions of the normative theory must face the empirical challenge, i.e. if you can derive from your normative theories that it is permissible to kill innocent children without any benefits, then there is probably something wrong.
Using this method, we have done quite a lot so far. We have established the UN Human Rights Charta, we have an elaborated system of international law, law itself being a manifestation of morality (denying the fact, that law is based on morality is like saying that technology isn't based on science).
Not everyone might agree and some say, "I think that chattel slavery is perfectly moral." And there are people who think that praying to an almighty pasta monster and dressing up as pirates will cure all the ills of the world. Does that mean that there is no absolute reality? Maybe.
Conclusion
As long as we have values, desires, dislikes and make judgements (which all of us do and which maybe is a defining characteristic of the human being beyond the biological basics), if we want to put these values into a logical consistent system, and if we believe that other minds with moral perception exist, then we have an absolute moral world.
So if we stop having any desires and stop making any judgements, that is if we lack any moral perception, then we may still believe in morality, as much as an agnostic won't deny the existence of God, but it would be totally irrelevant to us.
To the same degree, if someone lacks all the sensory perception, then the natural world becomes totally irrelevant to him or her.