After 9/11 state actors in different parts of the world and to various degrees decided to give security and counterterrorism measures priority over human rights and fundamental freedoms. In order to legitimize their policy choices, governmental actors used normative argumentation to redefine what is ‘appropriate’ to ensure security. We argue that, in the long run, this may lead to a setback dynamic hollowing out established human and civil rights norms. In this article, we develop a theoretical and analytical framework, oriented along the model of the life cycle of norms, in order to trace ‘bad’ norm dynamics in the field of counterterrorism. We conceptualize the norm erosion process, particularly focusing on arguments such as speech acts put forward by governmental norm challengers and their attempts to create new meaning and understanding. We also draw on convergence theory and argue that when a coalition of norm challengers develops, using the same or similar patterns of arguments, established international normative orders protecting human rights and civil liberties might be weakened over time and a more fundamental process of norm erosion may take place.