Do they really have time to think that through? Schopenhauer argues that in that instant the person has a realization that both individuals are one.
because I'm too lazy to retype the same ideas That helps explain "why" we tend towards seemingly "selfless" acts in the context of very basic instincts. But when considering the degree of "goodness" of an act is nigh onto impossible. One reason being what thedope pointed out, it's a sliding scale with no truly fixed points of commonality across all cultures and situations. Hence the need for varying "degrees" related to the criminal system. What Heat said is also very true from the perspective of the recipient of any acts of "goodness", a good deed is a good deed if the recipient views it as such. Yet for the person performing such acts, it is their personal intentions and motivations that define their character and any ultimate "goodness" or "evilness" concerning any specific action. If we look to the natural world without all our quantitative pigeon holing of everything, we see that everything is neutral and all acts are along the same spectrum of neutrality. Critters just be doing what needs to be done to get along, no good or bad about it. As thedope would say, everything strives to seek it's own good and comfort in the world. Sometimes that appears to be "good" to observers, other times not so much, but it always is us as the observer who quantifies the act, critters just be doing their thing.