The aim of this article is to highlight the role of religiously motivated ethics within the field of sustainability didactics. The article starts with critical reflections on the idea that religion, by proposing claims for knowledge of absolute authorities such as "divine beings or supernatural dimensions", offers capacity for uniting various ethical life-views and positions. An alternative position is outlined: religious claims of this kind rather have to be interpreted as democratic iterations, paving the way for constructive agonistic communication inside, as well as outside, classrooms where RE (religious education) and ethics education are carried out with reference to various dimensions of social sustainability. Such teaching contexts may be apprehended as "democratic communities" where religious justifications for ethical positions that refer to absolute divine or supernatural authorities could be seen as constructively challenging the borders for mutually respectful communication, and therefore as being important to highlight within ethics education on sustainability.