Brett McDonnell has an interesting post on the inherent ambiguity of "prosocial" behavior. His points are important, but I would like to rephrase and broaden one of them. Brett argues that "the question is prosocial behavior in whose favor? What if there are conflicting possible groups towards whom one might be loyal?"
As I understand the point he's making, it is a version of the broader problem that whether something is prosocial depends on your definition of the good society. On many issues, I suspect Brett and I would have very different definitions of the good society. He might think the good society promotes reproductive choice, while I might think the good society respects all lives whether they have been born yet or not. From this perspective, when you or I call something "prosocial" all we're really doing is using a 50-cent word that really means "pro how I think the world should be run."
To my mind, that pretty much evisverates any utility one might claim for the concept of "prosociality."