This chapter reviews some of the many possible harmful consequences of reciprocal actions. For example, people acting reciprocally for mutual interest can sometimes impose harms on third parties. Moreover, strengthening reciprocity and cooperation within a group may intensify their animosity towards outsiders, a possibility that is associated with nationalism, fundamentalism and many other harmful 'isms'. Indeed, there is even the potential for mutually reinforcing cliques to treat others who are ostensibly within the same broader group as outsiders, which may damage the collective. Reciprocal motivations can also be used as an attempt to obligate people against their wishes, which is particularly obnoxious when there are differential power relationships between those involved, and potentially undermines the very notion of a fair exchange. Furthermore, in relation to negative reciprocity, injustice may be felt if it is believed that the punishment is arbitrary or excessive, which can lead to spiralling retaliation and retribution, a spiral that is often very difficult to break.