This is the only law we need. Or rather, because it is a natural law, this is the only law we need to be aware of. It is known under many different names, but the point is that hurting other beings makes impact on the whole system and affects us too, as "the whole system" means everything and us. We are part of the world, we are not separate, no one is a lonely island... And a creature hurting itself is, for the lack of better word, insane. And confused. And not very smart. By the way there are few movies illustrating this, this is one of them.
To reiterate one crucial fact, natural law is not a "law" in usual sense of the word, not a human made up rule that needs to be publicly announced, enforced ever after and having consequences only when caught. Doing harm causes degradation of the whole system, invariantly and inevitably, regardless of whether we know it, understand it or believe in it. Like gravity, it is always present and active, even if consequences are not immediately inflicted upon perpetrator.
And the best part is that, unlike human-made laws which we might not even be aware of until some uniformed man charges us for breaking them, we have conscience, we have the ability to know right from wrong, we know and feel when natural law is being trespassed. The detector is conveniently built-in.
Unless... unless we identified with some role we play, like soldier, thief, politician, role that by design is in contradiction or denial of natural law. The thing is, we can chose to ignore consequences and implications of our action. We can shield ourselves from results of our actions (how often warmongering politicians go to war themselves? Or send their children?) What we cannot do is to make our actions not have consequences.
Cam it really be that simple? Of course. Despite of what we were told, the world operates on simple principles. When complexity is being introduced into legal/moral matters, we can suspect that someone is trying to control us, not help us. Now, what happens when natural law is violated?
Fear vs love
Love is a good one word description for expansion of consciousness.
Fear is constriction of consciousness.
Sometimes they are considered to be oppositions, but it's not quite correct - fear is simply lack of love, similarly to darkness being lack of light, not a thing unto itself. Love brings understanding, empathy, care. Fear is separation, aggression, suffering. Fear is consciousness withdrawing from mind, neocortex giving control to older parts of our brains. This is effect of broadly defined violence. This is what happens when natural law is violated.
What is violence?
We're taught slightly narrow version of answer to this question, so when asked we automatically respond with "physical violence": beating, killing (murdering, to be more precise), etc. Something we, as citizens and polite humans, are not supposed to do. But there are, of course, exceptions. Some people have special rights to beat and murder on the pretense that they uphold law and order or defend freedom, and violence inflicted by them is somehow just, justified, or even necessary. For an ordinary man though physical violence is generally prohibited, unless for self-defense, which is defined as defending from acts of violence performed by fellow ordinary man. Unless that fellow man happens to be in the role of mentioned earlier privileged groups.
It would be nice to think that "law and order" is simply natural law written down, but a) "do no harm" can be written down on only one page without looking stupid, and b) what law books contain is as natural as smile on Pennywise's face, and last but not least natural law does not need defenders or upholders. It is not human-made and it does not need humans to make it work, like gravity will not disappear, regardless of anything. Law and order is just a nicer name for control. Some people argue that our species needs to be controlled, lest chaos consumes us all, and although it is true that as a species we're still not completely out of our kindergarten, it is also true that there isn't enough effort done for helping humanity to grow up, be responsible, be wise, be free.
Kindergarten mentality
Some people say that we are deliberately being dumbed down and forcedly kept in baby chairs. I wonder how many of us have this feeling, aware of it or not, that something is not quite right with the world. "You don't know what it is, but it's there, like a splinter in your mind, driving you mad." It's simply our bottom being too big for a baby chair.
When you are in kindergarten there is some adult present who has control and can order kids around. Substitute parent. Kids might need that for some time, they need to be shown what it means to be adult, so they can grow up and become adults themselves. Now, this is what education and upbringing should be about. Unfortunately current systems are not designed to help children grow up and out. What they do is producing humans with enough knowledge to be obedient workers, good consumers and, most importantly, controllable by sticks and carrots. People spend their entire lives doing as their inner babysitter trained in their early years tells them. They carry in their heads that stick and carrot way of dealing with other human beings as the only and correct way. They think that punishment or threat of punishment is required for people to behave (or else there be chaos). Sadly, to some extend it might even be true, because someone who knows only stick and carrot, when stick is removed, tends to grab carrots with both hands with little regard to other people.
It's like Christians saying that without ten commandments people would kill, steal and swear, and atheists can't be moral, because they do not fear hell. Personally I'm rather afraid to be anywhere near people who don't kill, steal and swear because they believe in an invisible man watching them 24/7. But I digress.
So, we have carrots and sticks, although it seems that there are more sticks than carrots. If you work hard enough you can be rich, you can be famous, you can have influence, but there is generally a price in form of time or health. Rarely a carrot is free, for most people it's more a promise of carrot, never to be achieved. Sticks, on the other hand, are freely available for everyone. There are books of law full of sticks. There are offices full of people ready to use sticks if you fail to observe some "law" that they made up. And for many there is also the big, great, invisible carrot in the sky, and even bigger, invisible stick below ground. But I digress again...
Sticks
Violence does not limit to physical kind. Violence, in a very simplified form, is taking what is not yours. Simplest form of physical violence is taking a person's life, health, freedom of movement (we can agree that those things belong exclusively and non-transferably to that person?). Then, there is theft of physical property. Not necessarily connected to inflicting bodily harm, but it is also pure violence.
Then, robbery of time, resources, skills. All of that can be given voluntarily, of course, for a good cause, but in majority of cases "voluntarily" means choosing to spend 40 hours per week for most of your adult life just to avoid, well, starving to death. It is not a choice then, it is extortion, and yet job creators are considered saviors of people, which is irony that escapes most of us. Would you keep your job if you didn't have to perform it? If you had shelter, food, energy provided by, say, robots? In the same way as you have oxygen for free, it is there, breathe as much as you want, just don't destroy the planet? If there was no threat of taking away your house or property should you fail to pay your taxes?
Threat of violence is not essentially different from violence itself, it can even generate more fear than violence itself. Violence is control and control is violence. What would you do if there was no threat present in your life?
Violence and kindergarten mentality is so established and ubiquitous in our world that it is usually way beyond our perception and seeing it is like seeing fnords, one has to deprogram himself first.But once understood fully and correctly one can begin to think of getting above waves, getting out of the baby chair, firing your inner babysitter.
And to finish this paragraph there is one more important thing. When you realize the state of the world and you ask the question "who?"... It is important to remember that although there are hierarchies everywhere and power structures are like pyramids, even the higher levels of pyramids still belong to the pyramids. In power structure no one is really free. Oh, I guess it is much better to be on top than struggling at the bottom, but even if you swap places (like for example organize a nice, bloody revolution) you will still be confined in the pyramid. And the only goal worth pursuing is to be free to fly above pyramids, all the way to the stars.