Would Islam say that the norms of a society are the standards by which that society is to be judge if that society does not possess the Qur'an? Or by what standards does one determine that which is and is not morally acceptable in a society that does not yet have the Qur'an available to it?
(Obviously I am not talking about 21st Century western cultures, as they have the Qur'an available to them even if they subscribe to something else.)
With regards to morals and what is acceptable and what is not, there is a common denominator in all three major religions (Jewdaism, Christianity and Islam). All these accept as moral that which has been ordered to perform, allowed to perform or encouraged to perform. Be this of the request to perform such as be just, be truthful....etc, or of the abandonment nature such as do not steal, do not cheat....etc.
So in this respect, not only Islam but all the three religions share such points. So the standard of behaviour comes from God. When Islam came, it did not demolish these universal values, rather it refined and perfected them (from a muslims point of view). This is testified by the Qur'anic verses:
"If only the people of the Book had believed and been righteous We should indeed have blotted out their iniquities and admitted them to gardens of Bliss.
If only they had stood fast by the Law the Gospel and all the revelation that was sent to them from their Lord they would have enjoyed happiness from every side. There is from among them a party on the right course; but many of them follow a course that is evil.
O Apostle! proclaim the (Message) which hath been sent to thee from thy Lord. If thou didst not thou wouldst not have fulfilled and proclaimed His mission: and Allah will defend thee from men (who mean mischief). For Allah guideth not those who reject faith.
Say: "O People of the Book! ye have no ground to stand upon unless ye stand fast by the Law the Gospel and all the revelation that has come to you from your Lord." It is the revelation that cometh to thee from thy Lord that increaseth in most of them their obstinate rebellion and blasphemy. But sorrow thou not over (these) people without Faith.
Lo! those who believe, and those who are Jews, and Sabaeans, and Christians whosoever believeth in Allah and the Last Day and doeth right there shall no fear come upon them neither shall they grieve" (5:65-69)
So in these verses there is clarification that what was required by the nations before islam was that they abided by God's message. Now just like the Jews are criticised for not following the Gospel (Injeel-not the new testament), so the Christians are criticised too for not following the Qur'an. However, even though the Jews had the Torah (Tawrat) and the Christians had the Gospel (Injeel) they did not abide by it's commands (again in muslim prospective) and had they abided by them they would have been in the right path just like some of them who died before islam came about and followed their scriptures justly, their faith is not denied.
So for those societies that existed before islam the criterion is their book upon the original teachings of their prophets. After the comming of islam then we say: "O people of the Book! come to common terms as between us and you: that we worship none but Allah; that we associate no partners with Him; that we erect not from among ourselves Lords and patrons other than Allah." If then they turn back say: "Bear witness that we (at least) are Muslims (bowing to Allah's will)." (3:64)
In general this is what I believe and there are also other points and arguments but I think that this is enough.