In your opinion, are the best rules for society already known or something we are still figuring out?
By best rules, I mean just that. The most optimum set of laws for a society.
My personal opinion is that we will always be learning about ourselves and constantly having to adjust our theories because of that. We tend to try to make laws out of those theories as they become personal philosophies.
That's very difficult to answer.
If we take technology into account, then the rules will always have to be subject to change, because technology is ever-changing.
If we're talking about
fundamental principles of societal interaction... people are people. The most basic fundamentals of life don't change much from one culture or time to another. Almost everyone
wants enough to eat; shelter; safety so that they don't get killed too often; and some "extra" for the sake of security against an unknown future. After that most people want social interaction with fellow humans, revolving mainly around sex and/or reproduction, and status/influence/power.
That's putting it roughly... Maslov's (sp?) heirarchy of needs would cover it more accurately and in greater detail.
The fundamentals of a society are how to see to it that most people have a chance to meet those basic needs without resorting to force or threat too often.
Human nature is that most people don't want to work any more than they have to, unless there is a powerful motivating factor. It's been established beyond any reasonable question that societies that allow private property, and private ownership of one's own productivity and labor, produce in far greater quantity than societies that disallow these factors on the basis of collectivism/etc. That far-greater productivity means it is much easier for people to meet basic needs without killing each other over it too often.
IMO the above is fundamental to any society and that yes, we have a pretty good idea of how to structure such things as to maximize the benefits. That doesn't mean every society
does these things right or well; some are in denial, some are screwed up in other ways.
Now, the nitty-gritty details are another matter. These vary a lot from one culture or time to another. Things like who can tell whom to do what; who can marry whom and under what circumstances; whether you get to choose your fate or someone else does; what is polite and what is rude... all these things are certainly subject to change and the ebb and flow of philosophies, religions, fashion and frivolity.
Questions of degree, like
how much individual liberty vs collective responsibility;
how much private property vs public;
how much of your productivity you get to keep and how much goes to the "public good", and so on... these also vary depending on times and circumstances and societal winds and whims.
"If men were angels there would be no need of government." Well, not even that... if the vast majority simply followed the Golden Rule scrupulously and consistently, there wouldn't be much need for government. Unfortunately it often is not so.