Moral Relativism supports the perceptions of a specific society. If a society exists where it is agreed that someone should have their hands cut off for stealing a loaf of bread, then Moral Relativism supports the behanding as a "good" action resulting from the "bad" action of stealing. Another society may view behanding as "bad" and in fact the theft as a "good" action if the thief was stealing the bread to feed his family. Moral Relativism supports both viewpoints. No matter what the example is, Moral Relativism can support a variety of viewpoints on it depending on the society that it occurs in. This is "morality" of the popular sentiment.
This is what I am referring to when I say that Moral Relativism is no moral compass. A compass needle always points in one direction. If it didn't the compass would be useless for finding one's way. Since Moral Relativism's "needle" can point in many directions depending on society's mood. At one time, it was socially acceptable in the United States to own slaves. Today it is definitely not acceptable. Moral Relativism would have supported both viewpoints as being "moral". This makes Moral Relativism useless as a moral compass. Moral Relativism's big draw is to make people think that whatever they are doing is moral. Moral Relativism brings up ideas like situational ethics (e.g. sometimes it is acceptable to steal depending on the situation). Of course, this leads to the idea that "the ends justify the means". Most tyrants follow this belief.

The Golden Rule doesn't support Moral Relativism in most cases. The Golden Rule, "Do unto others as you would have them do unto you." instead supports the viewpoints of a (presumably) rational human being in a generic situation. Very few people (probably none) would ever want to be behanded, even if they stole something. As such, the Golden Rule would take a stand against behanding. The Golden Rule asks a person what they would want from a situation which is a question about their own desires. Yes, the Golden Rule is based, in part, on selfishness. It is also presumed that the person making the decision would be a rational person, and therefore not prone to answering something absurd. For example, if someone is considering stealing, that person would be expected to consider that if they were the shop owner, that they wouldn't want someone to steal from them. If the erstwhile thief were not rational, then they couldn't rationally answer the Golden Rule's question and may come up with some different answer, but generally speaking most people could be expected, in the generic sense, to answer the Golden Rule in a consistent manner, independent of their society (society being important in Moral Relativism). So the Golden Rule doesn't support moral relativism in all cases and cannot be equated with it.
Many people equate the Golden Rule with Jesus' statement to love our neighbor as we love ourselves. This isn't quite a good comparison. The Golden Rule doesn't say anything about love. If a person who hates himself is presented with the Golden Rule, he may answer out of hate and choose to injure others because he wants to be injured (yes, there are people that are this way). Jesus' commandment was to love and couldn't possibly be misinterpreted in this fashion. Still, as a moral compass, at least the Golden Rule will generally give consistent answers. So perhaps you would want to change the makeup of the idealistic country you were designing.

As to collectivism. I point you to one of dictionary.com's definitions:
That said, collectivism embodies the idea that the individual must submit their will to the collective. That the collective is important and the individual is much less so. A very extreme (artificial) example would be The Borg. That was a collective where the individual was completly meaningless and only the collective was important. A less extreme example would indeed be any sort of communist state where the collective defines all rules and the individuals are given enough to live and serve the collective.
Individuality has no place in a collectivist environment. The question that a collective asks is (always) what is best for the collective. The problem is that what is best for the collective often conflicts with what is best for a given individual. In a collectivist society, that individual loses. For example, if the collective is to survive, it is important that enough food exists. If there is a famine and not enough food to go around, the collective could argue that some individuals would be given no food (and starve) so that the rest of the collective can survive. Similarly, if a new "incurable" disease arises, the collective can vote to forcibly quarantine the minority with the disease so that the collective can still survive (of course at that point, the collective may decide not to spend collective resources to treat them because that would be taking resources away from those who had a better chance of survival).
These are not unrealistic examples. A society based on collectivism doesn't care about the individuals because doing so would always be at the expense of the collective.

As I suggested earlier. A balance must be struck between a completely selfish society and a completely selfless society.

-- Jeff

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"Government is not the solution to our problem, government is the problem." --Ronald Reagan