But Obi-Wan's reply about thinking in absolutes is the one that I really care about. It's the idea that gets closest to the heart of what philosophy is.
Any ethical question has a context. That context includes not only the immediate situation, but the principles involved. Here's the thing that both the "situational ethics" crowd and the absolutists get wrong: Principles are always absolute, actions and people never are.
A principle is always an absolute. It is not right or wrong, it is a fact in the widest possible context. Full-context facts apply to all situations. If you have what you think is a principle, but it varies depending on the circumstance, then it is not a principle. It may be a good rule of thumb, or a guideline, but it is not a principle. Principles are few in number. If you have a wide range of what you think are principles, then most of them are not actually principles, but guidelines.
On the other hand, every situation is different. You cannot ever create a principle that will by itself demand a specific action for any given circumstance, let alone a single principle that will dictate specific actions in all circumstances. You don't get off that easy - you don't get to dodge the responsibility of thinking and integrating in every situation.
You have to integrate the absolute principle with the specifics of the situation you find yourself in. It takes work, and there is a lot of room for error. But you have to try. Reality provides no automatic knowledge, and even in the light of absolute principles, the knowledge of how to act is always something you will have to work for.
Because this knowledge has to be worked for, and because there is room for honest error, a person - as a whole - can never be judged as absolutely good nor evil. Even a person's actions cannot be judged as absolutely good or evil (though in some cases they are so clear that the possibility for error is little more than theoretical). You cannot know all of the knowledge and context that person holds in his mind that led to his evaluation of the rightness of his act. You do have knowledge of facts, and those facts are never "gray", but you can't know that you know all the facts, or know them all correctly.
But more importantly, a moral judgement of another's act attaches to the person. An action just is once it is done, it is not itself good or evil, good or evil is an attribute only of a person, of one who commits an act. The judging of an act is the judging of the person who commits the act, at the immediate time of the action, and nothing more.
Yet there is an objective standard for judgement. Priniciples, are absolute. The situation in which an action occurs is absolute (it just is, it is not good or evil, it is just reality). All people and their actions must be judged against these principles as they apply to the circumstance. Your knowledge of these facts is necessarily incomplete, but you must judge nonetheless. You have to judge because your actions depend on the situation you find yourself in, and that situation includes both the actions that have come before and the people involved.
Judgement is evaluation, not condemnation. You judge only as a guide to future actions. It is irrational to expect your judgement to have any effect on anyone else - it is for you alone to use. But you don't get out of the work of thinking and integrating anymore than the subject of your judgement does. Your knowledge is as incomplete as everyone else's; you're evaluation is as subject to error as anyone elses. For that reason, your judgement of other people and their actions can never be absolute. Your judgement of these must always carry with it and additional judgement of how complete your knowledge is - what your chance for error is - that tempers the judgement with some level of uncertainty, even if it is infinitesimal.
But all judgements, whether they be nearly absolute or very uncertain, must resolve in an either-or way to guide your immediate actions. Before you can act, you must decide which side of the spectrum your judgement falls on. You may decide to delay action, or take some action that has fewer consequences, in light of an uncertain judgement, but even that is an action guided by an either-or judgement.
To fail to judge because of incomplete information - or worse because of intellectual laziness or a philosophical aversion to it - is irrational. You cannot act without judging whether your action will be right. To judge another's actions or overall moral qualities to an absolute degree is irrational - you cannot possibly know every single relevant fact with absolute perfection. To fail to use absolute principles as the standard of that judgement is irrational - it leaves you with no standard and no possibility of judgement.
Anakin and Obi-Wan were both wrong. "With me or against me" is an absolute juegement where no absolute is possible. Not thinking in absolutes when it comes to principles is just as wrong. However, both of them were right in acting on their judgements when they had to act.