"Moral philosophy is the effort to understand the nature of morality and what it requires of us - in Socrates' words, to understand "how we ought [emphasis mine] to live" and why."
I think Socrates hit the nail on the head. Morality, moral codes, ethics all have ideas on how people ought and ought not live. Many, many people think that morality is subjective, i.e. up to the individual to figure out for himself. If this is the case then any sort of behavior can be rationalized and justified by the individual. True, these same moral relativists will say that society has made up rules for people to follow, but isn't a society made up of individuals? Individuals whose morality is up to them? Furthermore what gives a society (any society, take your pick) of individuals the right to tell me what I ought and ought not do?
If the root of morality is the rule that there are no moral rules, it would be contradictory of a moral relativist to say that there are actions and behaviors that you should and shouldn't do. Yet, this is exactly what we see all the time. Out of one side of their mouth people say, "Well that's true for you, but not for me" and out of the other side saying, "You should not oppress the poor by harvesting their organs!"
Why is it that people have this idea that deep down inside there are things that are wrong? Not just wrong as in an opinion, but wrong as in wrong for all people in all places and at all times. Well, all people, no matter who, no matter where, no matter when, all people have the law of God written on their hearts (Romans 2:15). As creations of God all people bear the imprint of their creator and cannot escape it although many people will actively try to suppress this knowledge (Romans 1:18-20). It's funny that those very same people who believe that there is no God will feel that their rights are being trampled by those who claim that we 'ought' to follow God's laws! The only way the non-Christian can argue against the Christian God's moral standard is to assume that there are objective morals in the first place. And objective morals can only exist if God does.
* Page 1, The Elements of Moral Philosophy, sixth edition, by Stuart Rachels, McGraw Hill, New York, 2010
Note to self: I need to check on the correct procedure for footnotes. There might be English teachers reading this.