Imagine explorers from Earth travelled to another planet and found a civilization with a morality in direct odds to earth - where all manner of “perversions” were prevailing social norms, and immoral behaviour was what we would consider moral behaviour.
Would it invalidate our prevailing morality, given that there is obviously no universal moral system?
i would postulate that earth and this other planet have something in common…
The unknowns still exist.
Wow, so many possible angles…
Are we talking practically or possibly here (ignoring the question whether the second has any real meaning without the first).
Possibly:
No - They are immoral, we are right.
No - Moral systems arise from communal living, their ‘moral’ and our ‘moral’ are both equally valid due to obviously mutually exclusive methods of moral action-creation (arg that’s cumbersome). Both merely ‘are’
Yes (sort of) - All morality is contingent. Contingency is meaningless, ergo our morality is meaningless. The other system doesn’t make it so merely illustrates it.
Practically I find more interesting. You talk of ‘discovery’, do you think that until alternatives are discovered our system is valid? That only concrete examples can challenge morality? Interesting that this is bound up in a thought experiment 
.
Anyway, the best practical answer would probably run: no / question is meaningless, going something like this:
There ya are. Not very well thought out, could do with more detail, but my initial response to your problem
You must be easily corrupted, or you wouldn’t care for such a question as that!
Obviously, survival would the the goal, but what is the strategy to attain that survival? Working for the establishment of good order. That benefits both the individual and society in general. The only ones it doesn’t benefit are the anti-social goombas and the megalomaniacs who want control, even if it means a scorched earth and the degradation/destruction of the species. This strategy requires a morality/moral code/whatever that supports this strategy. And that moral code must not be based on any type of double standard. That just enables the dictatoriacs.
So to answer the original question, I’ll have to have the answer to another question: what possible logical basis could there be for such a moral code as you pose? (Anybody who says their God told them so doesn’t understand that dictatoriacs will actually lie about such s**t get their way. Imagine! 
For the uninitiated, it’s called demagoguery.)
I agreed with Phoebus. Morality in its broad form is simply an extension of pro-cohesive social behaviour. And as such - adaptive - an ‘immoral’ primitive group would die out early.
That planet you mentioned would have to be an ancient apex society, which had long ago fixed its population problems vs. simple survival and essentially was exploiting its ‘surplus’ population for the purposes of entertainment. Immortals get bored.
Why would such a society have a “surplus” population? If China can control its population, I feel that some more ancient, far more intelligent society could control its as well.
I agree with the ‘morality = pro-socially cohesive behavior’ idea. But that being true there would seem to be some forms of behavior (behaviors which advance the odds of group survival) that might obtain a sort of universally moral status.
Take ‘murder,’ for instance. Is condoning murder ever conducive to a group’s survival? What about the group’s condoning lying or stealing? Would that ever work?
What gives a group its best chance to survive: to relate to the external world in the way in which the group wishes the external world is or to relate to the external world in the way in which the group can best KNOW how the external world is?
If it’s the latter – and I believe it is – then the search for truth (i.e., the search to know reality as well as it can be known) has to be one of any group’s great moral precepts.
First point, genetic pre-conditioning for survival as the basis for morality entails no universal moral codes that are either rationally acceptable (i.e.: rape is fine!) or non-contingent. By the latter it is almost universally held by humans that incest is bad (big genetic no no) however on one island somewhere in the south pacific it is considered fine because of their limited population. It creates one universal, the will to life abstracted for a community of a minimum of one.
Second, knowledge is irrelevant to our actions if they arise from drives as to act on that basis is to act non-rationally, knowledge only comes into play after the event as an act of self-interpretation. There is just you, there is just the act, then you think about it.
Sure, I can envisage societies in which rape might be considered perfectly acceptable behavior. But that’s an easy one.
A much more difficult proposition is murder. Is murder ‘fine’? Can murder (i.e., the unlawful killing of a member of one’s species with malice aforethought) be acceptable behavior in any community which wishes to propagate?
Sure, gene survival morality manifests on three levels: personal survival, community survival, inter-community survival
Personal: ‘I’ vs ‘Them’ (as a generalised ‘you’) easy to murder since you prioritise yourself
Intercommunity: Same really as personal but it’s ‘we’ not ‘I’ that is the definate particular. Both are generally defined by external threats. It is okay to kill them because ‘they’ (and by abstraction ‘you’) are not ‘us’. Generally this us is tied up with concepts of human / what it is to be ‘good’ and the them is bad, less that human
On the middle level, on murder with respect to people within our community (to murder another one of us) generally frowned upon, usually the most punished, but still occurs where the victim is seen as a threat. I don’t have a concrete answer to give though, it is probably somewhere in the grey zone between different absolute responses.
If the victim is seen as a threat or seen as not a member of the community, then the act is not murder. The act, instead, is merely a killing.
To commit ‘murder’ in the sense I am using ‘murder,’ an act has to meet certain requirements. One, it has to be committed by an individual who is seen as a fellow member of the community upon an individual who is seen as a fellow member of the community.
Two, the act has to be committed with malice aforethought.
Three, and perhaps most importantly, the act has to be viewed as an unlawful act by the larger community.
Thus ideas of murder between us and the amoral aliens cancel one another out - it is shown to be an entirely socially constructed concept.
Well, I disagree with your definition of ‘murder’. Sort of. That sentence sounds rather petulant so let me elaborate:
I almost entirely agree with the premise that murder, as outlined above, will almost always be ‘morally’ wrong. Mostly because I can’t think of a situation that isn’t so alien it becomes useless to discuss in practise.
However, I would argue that your definition excludes certain ‘killings’ it shouldn’t do as a definition of murder. The flaw is that, in a ‘group’ of people, anyone who kills will either be acting against someone who has been externalised / dehumanised by the community, or will be externalised / dehumanised themselves. They might have been members of the community at one point but they stop being, and often stop ever having been (the past is re-interpreted), when they are killed / kill. Their past actions are re-interpreted based on new behaviour. Which means your first premise always denies murder. If you see what I mean .
On the other hand, I’m not sure what you’re trying to say here, please elaborate
Most likely thus validating all along that we live in a purposeless existence guided by aimless relativity.
( In short: nihilism.)
I may misunderstand you, but you seem to be saying that if the definition of ‘murder’ excludes some killings then the definition of ‘murder’ is flawed. But how can that be since any definition of ‘murder’ excludes some killings?
Armed combatants kill other armed combatants in war but that is not usually considered to be murder even though it definitely is considered to be killing.
I’m afraid I don’t see it. I see no reason to believe that all murderers are either externalized/dehumanized individuals themselves or that they murder only those whom they believe to be externalized/dehumanized individuals.
I agree with you that such does occur, but to believe that it is the case in every murder that is committed seems to strain credulity. I can think of any number of cases in which murder victims are considered to be fully qualified members of the murderer’s own community. People murder for reasons of envy, greed, uncontrollable rage, etc. They murder for lots of reasons that have little to do with their psychological image of their victims.
It’s really difficult to imagine a society in which the unlawful, premeditated killing of other innocent members of that society is considered to be a moral act.
That’s really my elaboration right there.