In peer-to-peer overlay for video broadcast, peers contribute a portion of the bandwidth to the overlay in return for the service. In the presence of network heterogeneity, it is not well understood how much bandwidth peers should contribute and receive in return. Existing protocols implicitly assume peers are either completely altruistic (which leads to fairness concerns) or completely selfish (which leads to suboptimal performance). In this paper, we argue that altruism should be explicitly considered. We propose a policy framework in which a wide range of altruism can be modeled and parameterized. The key findings are (i) the level of altruism has significant implication on the overall performance of the receivers; even a small degree of altruism goes a long way in improving their performance, and (ii) a wide range of altruism policy can be implemented efficiently in a distributed fashion. We validate these claims using simulation, with traces from real Internet broadcast events...