So the problem seems to be not when someone murders, but when there's no clear cirterion to murder... is what some of you were trying to say?
But I wonder if that can be catalogued as morality. I'd bet that if you could made an experiment with chimps, where one chimp in the community started killing other chimps without reason, the other chimps won't tolerate him well.
And I would not say that chimps have morality.
What for me seems a big problem, is that, if I really want to kill some people, and justify myself from a moral point of view, why couldn't I invent a "valid reason" for which that guy should be killed.
I want to point out that there are cases in which murder among members of the *same* society is well accepted:
1. A turkish dinasty: when the head diead, the heir was not only allowed but obligued to kill all his brothers and even cousins, everyone who could have the minimmal reason to aspire to the big position. Of course, there was a good reason: you had to avoid any possible internal conflict for power and there would never be internal wars.
2. mexicas. If the astrologist said that you had to be killed, you had to, and, if that was said at the moment of your birth, it was not important what your position were in society, and you had to be happy cos your destiny after death was gonna be best one. Every now and then, the priests dictated a certain quantity of humans to be killed.Of course, there was a good reason. The Sun god needed human blood to feed and keep having energy to rise every day and allow plants graw and the majority of people could live thanks to that.
What really worries me is that, human being is the only animal that can invent "good reasons".