That is tantamount to making excuses for their behavior.
The deeper nature of the crime is the same, the only differences residing in the more superficial nature and the degree of the offense. Handing out parking tickets is, at its deepest roots, no different than murdering an unarmed suspect by shooting him in the back. But to see how this is the case, one must be able to strip away all arbitrary superficialities and get to the absolute core principle at work. In this case, it is the fact that one human being is imposing an arbitrarily contrived requirement upon another. It is done without consent and no other demonstrable authority. That is the core nature of the crime and it comes into play no matter what the other elements of the act in question may happen to be.
Is a crime a crime if the social paradigm doesn't recognize it as such? Of course it is. "Crimes", the unprovoked violations of the life, liberty and property of others, like the principles from which we deduce them, are objective and self-evident. To an extent, I'm undermining my own argument here, but we have to recognize the power of social conditioning - you and I may have been born sovereign, but from the moment we could understand language and begin to reason, we were inculcated into the "authority" paradigm; Empire, as you eloquently refer to it. We had to be "born again", accepting the truth of human nature and interrelations. And now when we speak of that truth, the vast majority of those around us look at us as though we're from another planet, such is the power of our perverse social paradigm. Plato's freed slave returned to the cave and told those still chained to the wall of what he'd seen outside, and they thought he was mad. Acknowledging self-evident truths isn't a perilous journey from bondage in cave, granted. But upending everything one has been taught to accept as true is no walk in the park, either, and most people haven't made the effort... hell, most people don't even know there is anything to upend! Fish don't know they're wet, and all.
So, yes... they are criminals in that they in nearly all cases violate the life, liberty and property of innocent people. But, yes... they are little more than children, without a developed ability to reason... they have no
reason to reason - everything that they've been taught from the moment they began to understand language leads them to believe that they are doing "good", and the vast majority of people in our society stand behind them, and tell them it is so. To kill such a person - outside of self-defense - is tantamount to killing an idiot, or a child.
Murder has a specific meaning. You're being hyperbolic here. Killing enemy soldiers is not murder.
The only morally justifiable killing is in self-defense.