Each character in "Watchmen" has a different moral code, which motivates each character to have a different stance on good vs. evil. Throughout its story, Watchmen presents several takes on the morality of murder, the ultimate judgment of death, and its implications in the grand scheme of the world. At the end of the graphic novel, only one conclusion can be drawn; there is no moral justification for killing, only the justifications that individuals place upon it.
"Who watches the Watchmen?"
Rorschach represents a black and white morality system. For him there is no grey area, any bad action must be punished, regardless of what good will come of it, which is the reason he cannot ever come to terms with Ozymandias's plan. He does not care about humanity, only justice, and is willing to allow humanity wipe itself out in order to maintain his ideals. He sees all the evil around him and has made it his life’s purpose to extinguish it from the world at any cost. He takes an uncompromising approach to fighting crime, punishing all no matter the severity of the offense, he is the judge, jury, and executioner of his own morality. He wholly relies on his own judgment to determine who lives and who dies. Rorschach sees the world as a blank slate, without an inherent set of moral standards, just the set of morals each individual places upon themselves. This theme is common throughout the narrative: each character has their own view on their role in the world and how to "improve it."
As can be seen here, Rorschach has a very strict moral code, he believes all of the city has sinned morally without punishment, so they don't deserve his salvation. A classic example of Rorschach's strict uncompromising morality.
Adrian Veidt represents a sort of "scale morality" system. He believes an action is good if the goodness of the action outweighs the bad. This is his main reasoning behind his master plan, he gives people cancer, and kills the comedian along with millions of New Yorkers in order to prevent World War III to obtain peace among nations. He ignores short term harm for long term benefit and only cares about the final consequence.
Here, Ozymandias reveals his master plan and the basis behind it, he feels the needs to kill millions so that billions can be saved from potential nuclear disaster.
Dr. Manhattan lives in the past, present, and future simultaneously, is immortal, and has near unlimited power. Because of this he is almost entirely disconnected from the human condition, has little sense of morality, and find's human interaction insignificant and many times tiring. He would rather sit on Mars alone than save millions of humans. Manhattan has god given power, but perceives that he is powerless against the flow of time. He doesn't think there can conceivably be a right or wrong, it's all relative to other meaningless things, so he just chooses simply not to act.
This shows Dr. Manhattan's indifference to life and death on earth due to his detachment from something as tiny as human existence in the scope of the entire universe.
The comedian's perception of morality is based on the fact that every person's moral system is based upon personal opinion, there is no fixed right or wrong so morality doesn't exist. He chooses to become a "parody" of what he perceives the world as, a jumbled mess of conflicting moral bases. To him, the idea that someone as morally bankrupt as himself could be considered a hero is hilarious, and he deliberately plays it up because nobody ever tries to stop him.
Here is the Comedian (Eddie Blake) showing his moral system of doing bad and not caring because the U.S. want's him there, taking advantage of the government's moral holes.
What Does it All Mean?
All of the different moral systems in Watchmen can lead the audience to many different conclusions. In the face of right and wrong every person has a different, subjective, moral system. Actions cannot truly be judged through a moral lens. Each moral system of each character is pushed to an extreme to explain the illogicality and harm of each system if not in check by other moral systems. This might be an allegory for the United states government to explain the actions in World War II. Truman's view, shared by Ozymandias, was to drop the bomb and sacrifice hundreds of thousands of lives for peace and the end of the war. The other characters show what happens when you push other moralities to an extreme. This is an underlying question behind human existence, what is good and evil, and who decides what is right? This question is unanswerable, and Watchmen realizes that and offers potential lenses to look at each of these moralities, it is up to the audience to interpret which on is best and which one achieves the most goodness in human existence. The famous quote, "Who watches the Watchmen?" demonstrates this ultimate question and proposes that there is no one form of morality that is right, each one has their own flaws and downfalls and it is up to each individual to decide which is right for them.