I've seen enough of these threads to try my hand at it so here goes:

Good and evil do not exist as isolated entities but are human constructs insofar as they are labels used to condemn or praise actions.

However, this does not mean that good and evil things would not happen if it weren't for our imput:

The killing of innocents is, under most biologically and socially evolved (evolving on both individual and group scales) moral systems, considered wrong. (Unless, of course, it is done in the name of achieving a higher goal.) Yet it still occurs whether we know about it or not, and in imagining such an occurence happening without our awareness, we know that "evil" things can happen with or without our personal presence or knowledge.

Good and evil are not fixed values but fall on a scale. One action (murder) can be more wrong than another (stealing). The extent of the perceived wrongness of a particular action can vary slightly from person to person but will still be percieved as wrong in the greater society.

Being moral can be trumped by more important concerns (ie survival) and even, studies have shown, obedience to authority (Milgram experiment) or punctuality (Darley and Batson). This does not mean that the person who acts immorally is evil, since absolute evil does not exist. We are all victim of circumstance, which in turn influences the morality of choosing a particular course of action.

Religion uses absolute good and evil and the concept of punishment or reward in the afterlife as an additional incentive for people to follow religious commandments in addition to gut feelings about morality. This helped regulate people's behavior when societial groups became too large for tribal "courts" to effectively manage people for the sake of group survival.

That's all folks.