The way people throw their rights and wrongs at you these days, it seems as if morality is something more than just a purely human concept. In reality, it isn't. You can shout, scream and hold signs all day showing your vehement opposition towards abortion, because you think it's wrong in terms of the moral framework laid down by your sky-fairy; but simply put, repetition doesn't make it any more real.
One could argue that a moral framework is an absolute necessity for a functioning human society, but don't let that though fool you for a second. Moral rights and wrongs don't only differ from society to society, but they change over time. The most important aspect however, is how morality changes with power.
To elaborate on this relationship, we need to see what motivates and influences human actions. One factor that influences actions is how favorable the consequences of that action turn out to be. Are they optimal? Are they optimal only to the human entity causing the action? Are they optimal to entities directly or indirectly related to the human entity causing that action? So we see that some people think only of themselves, and some people think about people surrounding them, the environment and so on. Between these extremes lay people with mixed emotions.
A second factor that's more important, is whether that human entity making a decision favors order versus chaos. Someone who decides to do the right thing, isn't doing it simply because it is right, but because they believe that by producing more order, they are decreasing the consumption of chaos; in other words, they prefer order because it assures them order. A person who refrains from threatening random people with a knife does so because it reduces the probability that someone else will do the same to them. In an economic sense, you can think of these people as risk-adverse. Similarly, there are people who tend towards chaos. The magic of the unknown thrills them. Not knowing the outcome of their actions influence their decisions. Like a risk-loving person playing a gamble, chaos influences the actions of a chaos-loving person.
Morality then, is influenced by the consequences of actions, how these actions affect the self, and how orderly or chaotic the self is. Nothing besides these factor actually matter at all. In a hypothetical society where rape or murder is the norm, these same factors influence the morality of any given entity. The outcomes of all our decisions specifically decide how much resources we can consume, and our personal moral decisions are heavily influenced by the outcomes. The outcomes in themselves are not important, but how much resources they help us attain.
We can think of this in another way. Comfort. When you lack the very basic necessities of survival such as food and shelter, your moral perspective changes radically. You are then not concerned with the morality surrounding stealing food or annexing shelter, but you are concerned only with the outcomes of your actions and how they will affect your consumption of resources, ie. food and shelter. In another comfort zone, when you have all the basic necessities for survival, your thoughts on moral good and wrong become stronger. This is because you already have the minimal level of resources required, and any further actions you take cannot have outcomes which will greatly reduce your comfort-zone. This is when it becomes wrong to steal or take bribes.
In a way, moral frameworks exist to produce an optimal output of order for any given society, and people within that society attempt to act within this moral framework in such a way as to maximize their own consumption of resources. Rape isn't any more right or wrong than philanthropy . Murder isn't any more wrong than helping poor people. People perceive actions as right and wrong only because the morality surrounding a given action in a given society influences their own actions.
But you know why it's okay to lie, cheat, kill and rape? Because if morality was indeed tied into the very fabric of time and space and universal laws of physics, then committing a wrong would make you disappear in a puff of vacuum. But since we know that doesn't happen, everything is a go, as long as your actions have favorable outcomes. :)