Harm is a way of life.
moreno—[do no harm] may be only something to think about when you have a choice before acting…
like to kill or not to kill…
If killing wasn’t against the law more people would be doing it.
why is killing against the law…
OK. I read the OP as suggesting it was a guide to behavior in general. But don’t doctors and police and citizens of countries with or without armies still have choices? Aren’t there conscientious objectors and pacifists? The british police used to not have guns - I don’t know where they are at these days. Of course they did harm with their clubs or whatever they had.
But if you meant Do no harm when you have a choice between hurting someone or not hurting someone and there is no (good?) reason to hurt them, then I am closer to some agreement.
But the rub is in the rationale and this is left untouched by the guideline.
the guideline is a suggestion not commandment.
it is up to each indvidual how it would be useful to them…
I think, unfortunately, they already do use it.
I’m sure Hitler thought whatever harm he did necessary. And also has rationale to discount harm - since Jews were not really human for example, more like rats and most everyone will kill a rat in their house.
And for any sloppy readers, I am not suggesting Hitler’s rationale was good.
Because those in power don’t like individuals disrupting their organization of things where they think to themselves that only when they want to kill others in the name of organized warfare is it ever ok.
(There is also the occasional political assassination and of course the hired police that enforces the state’s will on everybody else that from time to time have to kill those individuals that don’t give up resisting that become practically unmanageable by authorities.)
(Then of course there is the state’s executioners in prisons that tie down defenceless individuals in restraints by terminating their lives in a sort of symbolic gesture of illustrating the ultimate fate of what happens to rebels that take their individual rebellion against the rest of the world too far. Those are the individuals that disrupt the organization of authority so very excessively or severely that their bodies symbolically have to be disposed of in order to send a message to everybody else of what happens to anybody that dares challenges the selected order of things.)
Killing is only ok when it is approved by those that control the state. Controllable killing through the state or government is good but uncontrollable individuals killing randomly is considered bad. It’s all bunch of authoritarian red tape absurd taboo style bullshit if you ask me. I say let’s just level the playing field and start letting everybody kill each other equally. It worked for neolithic human beings. Why not for modern ones?
It’s all about hierarchy and submission. Remember that those at the top of pecking order can kill without impunity but those at the bottom cannot since they are reduced to just work their day jobs being told to quit their whining lamentations and to just shut up into silence. 
Now your getting it. 