Before I move on and discuss moral relativism at the cultural level, I briefly wanted to point out something that Michael Shermer (atheist, relativist, and editor of Skeptic's Magazine) said in a debate about moral relativism. His take is that, even though there is no God, our morals are absolute, handed down to us by evolution. I definitely disagree; if no God exists, evolution certainly can't hand down to us moral absolutes.
Anyway, in this debate, he and his opponent were discussing the rape example. He said that the rape would be wrong no matter whether there is a God or not. I thought that was interesting, because he was presuming there is no God.
He is claiming that there is something deep down inside of us such that we "know" that the rape is wrong.
THEN he says it would be wrong whether or not there is a God. Do you see the fallacy here? His argument is entirely based on the fact that each of us knows it's wrong, so it must be wrong regardless of whether God exists. What? That is what's called circular reasoning folks. Let me step you through the circle.
Presumption: there is no God. Observation: we all feel that rape is immoral. Therefore, some sort of moral absolutes exist inside us, even though there is no God. Conclusion: you don't need God to explain moral absolutes.
Actually, what he's just proved is that you can convince yourself that moral absolutes can exist whether or not you believe in God, which of course has no bearing on the existence of God.