In situations of violent group conflict, group members often argue about how to deal with the outgroup. While some argue for aggression, force, and separation, others argue for negotiation and cooperation. Each side attempts to persuade the group that their own position is normative and is most in line with the interests and essence of the group. These arguments often involve denunciations of opponents as disloyal or deviant. In such situations, definitions of group identities and norms, and what counts as loyalty and deviance, are therefore disputed. This article analyses how a UK-based Al-Qaeda-supporting organization denounces 'moderate' Muslims in the United Kingdom who engage with secular institutions and who ally themselves with non-Muslims in political disputes. Drawing on theological, historical, and political arguments, a prescriptive norm is constructed whereby the correct behaviour of Muslims in the West is to avoid participation in secular political systems and to avoid political cooperation with non-Muslims. Muslims who are seen as breaking these norms are denounced and denigrated in a variety of ways by assigning them a range of deviant identity positions. Denunciations involve explanatory accounts which construct opponents as unworthy representatives of the group based on their deviation from Islam, or from ignorance, cowardice, mental weakness, or self-interest. This article illustrates that the practice of denunciation is an important aspect of the organization of group conflict. Finally, it argues that it is dangerous for social psychologists to treat group norms and prototypes as consensual.