There are things which are subjective, but universally subjective based on the human condition. The universe doesn't distinguish between two different electrons, but to a human the electrons in his brain are way more important than ones in a rock and that is a phenomenon that any human will agree to. It's a bit silly to call something subjective when all humans everywhere agree to it.
All human cultures that have ever existed draw a strong distinction between justified and unjustified killing. If you're walking down the street and some crazed killer tries to murder you, any civilization that has every existed would agree that killing that person in self defense was justified. This would apply to modern America, ancient Greece, Nazi Germany, the ancient Inca Empire, tribesmen in the Congo, medieval Europe, and so on. Many of those societies allow for killing under conditions which we do not approve of, yet they still condemn murder under mostly the same circumstances. Of course, there are gray areas and where various cultures draw the line has been different, but the basic idea remains and it is effectively universal.
Of course, killing being lawful isn't the same as being moral and that is another philosophical Pandora's Box.
