Final answer:
Cultural relativism is the cultural theory that rejects ethnocentrism by promoting the understanding and evaluating cultures based on their own merits.
Step-by-step explanation:
The cultural theory that rejected the idea of ethnocentrism is cultural relativism. Unlike ethnocentrism, which evaluates other cultures according to the standards of one's own culture, cultural relativism encourages the understanding and evaluating of other cultures based on their own merits and contexts. It advocates for the appreciation of cultural diversity and the understanding that no single culture is inherently superior to any other. This perspective is essential in anthropology and sociology as it allows for a more objective study of various cultures without imposing one's own cultural biases.