There are two broadly distinguishable approaches to justifying altruistic concern. Under the first approach, there is an obligation to be altruistic. The reason we should be altruistic is that this is what morality requires of us; failing to do so would be morally wrong.
The second approach stresses that being able to make a significant difference in the life of others is an exciting opportunity. On this approach, emphasis is given to the fact that altruistic actions can have a large positive impact on others, as well as improving the altruist’s own life.
“Excited” and obligatory altruism are not mutually exclusive perspectives: one could think improving the lives of others is both a moral obligation and an exciting opportunity.
Karnofsy, Holden. 2013. Excited altruism.
An articulation of the “excited” altruism perspective.
Singer, Peter. 1972. Famine, affluence and morality. Philosophy and public affairs 1(3): 229-243.
The classic exposition of obligatory altruism.
Wise, Julia. 2013. Cheerfully.
An example of the “excited” altruism perspective.