This is an idealized theory. Fact of the matter is that altruism comes from a subconscious expectation of reciprocation. It evolved because people who stick together are generally more successful at life than people who betray each other. When you are nice to someone, you are saying "i accept you into my social circle, and I will offer you the benefits of friendship." Whether or not you care to admit it, this is an investment. "If I am nice to people, then they will be nice to me".
Otherwise, everyone would just eat everyone else's babies.
Seriously though when someone breaks the cycle, everyone who has invested in them in the past feels slighted, and are less likely to extend the hand of friendship again in the future (documented studies show this also occurs in squirrel communities).
You may not expect something right then, but you do expect your kindness to be remembered, and it is offensive when it is not.
This certainly has nothing in common with what motivates me. To assume that all people share your values is a mistake.