Soldiers life threatened by his own side.

[liam]

A right drawn from any given society is not subject to relativism? News to me.

It certainly isn't news to you, I am sure you have heard of 'human rights'.
The problem I encounter in cultural relativism are as follows:
-It proposes the idea that morals are determined by society (as cultural relativism would propose), yet morals determine the way that members of society behave so we arrive in the circle of morality being due to culture formed by morality formed by culture formed by morality etc etc so either we must dismiss cultural relativism or accept infinite regression (an illogical concept).
-Cultural relativism would allow for the acceptance of completely immoral customs simply because they are the norms (such as murder, slavery and rape). These are bad actions but would not only be permissible but, according to cultural relativism, potentially moral. This is abhorrent behaviour and cannot be permissible.
-Cultural relativism asserts that cultural customs may make acts moral but this would also allow for sub-cultural norms to be permissible, including counter-cultures, meaning that an act may be moral and immoral in the same social situation and may be further reduced to sub-sub-cultures and so on, meaning that we encounter examples whereby conduct within certain groups to be multiple levels of contradictory (moral and immoral and moral and immoral &c &c). This would mean that in posing the question 'is X moral?' we encounter an answer of both yes and no, one of the most fundamental logical impossibilities in philosophy.
(there are more but I'm trying to moderate my response length)

Thus we are far better concerning ourselves with universalisable morals than cultural ones as these are dysfunctional.

Society exists therefore rights must necessarily exist? News to me.

That is not my argument? I was simply concurring that rights can be drawn from society.

Isn't the notion that we must do what "best serves society" just an assumption on your part?

I did not say that we must do what serves society best, I do not believe you understood me correctly. Rights, by their nature, do best serve society as they maintain the moral integrity of the people which constitute the society itself. Let us say that a society of 100% deontological people exists (thoroughly hypothetically of course), these people will, through their moral behaviour, benefit society as they will enforce no dogmatism on others, manipulate no others and commit no acts that are generally detrimental to society (such as murder, rape or theft, for example). Thus we can say that these rights do best serve society, but not that we must act to best serve society.