I have always disagreed that Good and Evil are subjective terms. Let us take Good as an example.
To begin with, there is no definition of Good. Good just Is. The same, for instance, can be said about a point or a straight line in Euclidean Geometry: there are no definitions to describe them as they exactly are, though everyone knows what they are. If we are to examine this from another perspective: No one has ever seen a perfect point, nor a perfectly straight line; despite this, everyone knows what a point and a straight line are. Therefore, what we may presume at this point is that for every object there is one Idea, one Form, one Archetype, call it however you like, and this Idea may be manifested in the physical world through many different and imperfect things. For example, the Idea of Good is one and only one. Good, however, may be expressed as many different things; as Oriens has said, in the Mayan culture, it was considered Good to sacrifice a human for the shake of a god and in ancient Greece it was normal for for a man to form a cross-generational relationship with a minor. For the modern and "civilized" person, the above would be characterized as being rather Evil than Good.
Because of this, one might say that Good and Evil are subjective terms, perceived differently throughout the course of History. As I said previously though, Good and Evil are two definite things and Man always seeks to reach Good and distance himself from Evil. Then, you may ask, if this happens, wouldn't Good and Evil be the same for everybody? Not necessarily. See Good, for example, as the top of a high mountain and imagine that there are many roads which lead to this top, meaning that there are many ways to approach the Idea of Good which, no matter how many ways there are to approach it, it is one.