War and killing

Question: The Qur'an says its okay to kill your brother/fellowman if he is spreading discord, or has committed murder, infidelity, or adultery. The Old Testament permits certain sins in certain conditions. The Laws of the State invariably allow certain crimes to go unpunished when certain conditions instigated thecrime, such as self-defense or the defense of one's property or family.
All of these exceptions to moral law are instances of the ends justifying the means, the circumstances or conditions of an act serving to justify the act itself. We consider it morally reprehensible that a man should not go to war and murder or be murdered for the cause of his government and the propaganda they espouse. As long as he is following lawful orders, a soldier is not held in any moral accountability for actions which are commonly unacceptable, such as killing another human being, ruthless destruction and theft of property, kidnapping, arson, etc.
A question we must ask and answer is when is it proper to break a moral law, many of which are commonly accepted across diverse cultural boundaries? Who can permit the commission of harmful or sinful actions and set the conditions upon which those actions are permitted? Is it proper to say that only the source of a given law has the right to set conditions upon which that law may justly be broken?
Perhaps we should focus our examination of this question upon a specific category of laws such as those laws that forbid a person to take another person's life; that is, forbid a person from committing murder.

Another questioner responded: I'm up for that. Why is something committing murder, which clearly against the law not considered morally incorrect in war? It is not just OK to kill, but is required.
I am a pacifist and can't understand taking young men (and women) with every potential in the world and making them do the unspeakable in addition toputting their own lives at risk.
How is this justified?

Answer: As I understand it, its only okay to fight in defensive wars, not offensive. Protecting oneself from danger is a basic human instinct.