I don't think "legality" is going to be of any help. Laws and Rules are concrete and easily defined. "You do this...you get this punishment." (Or at least that's how the legal system should work...if you think that's how it does you're fooled

). Laws are society based, just as morals. But Morals aren't as easily defined. We here in America think there's something wrong with walking around nude, or breast feeding in public, my understanding is other places around the world think nothing of it.
But I would disagree with
Fea in that just because morals are society based and more "opinionated" doesn't mean that since you find this act right, that means it can't be the "bad" thing to do. Sauron found it right to control the world and make everyone his slave, doesn't make it good, as Tolkien would say that is indeed evil. So, which brings I guess to the question of what is wrong and what is right?
Morals and "what is wrong" I think are to different things. I'm sure I hold many things of what is moral and what isn't then my fellow BD companions. But, what is evil is the harm of someone else, that is what "evil" is and that's what makes Sauron evil. Just because he wants to make Middle-earth his dominion and he thinks that right, that doesn't make him right. It makes him "evil" because he brings harm to others. It's the "crossing the line" so to say, when what you think is good crosses over and harms others.
Morals aren't so clear cut and dry, but what is good/evil is I think much more concrete.
Edit:
So I guess I'll give an example of what I'm meaning to say, as I think I jumbled and rambled some nonsense.
Let's go back to the nudity example. Americans think walking around nude is "wrong" while other cultures don't find it wrong at all, it's actually something more spiritual. To Americans that's not moral, we shouldn't be doing that.
So, let's say since I find that "wrong" I went around killing and mass genocide people who walked around nude in public. Now that would be what evil is. The crossing the line, crossing over into other peoples morals. I crossed the line and said "since you don't agree with me I'm going to bring physical harm to you." That is what I find evil and the difference between what is moral and what is good/evil. (Please don't think I'm going to going to go around killing people who walk around in the nude now

)