Keep these straight
Ethnocentrism — judging another culture by the standards of your own, as though yours were the natural measure. Everyone starts here. The mistake is not having the reaction; it is stopping there.
Cultural relativism — Boas’s method: explain a practice by its own culture’s history, environment and meanings first.
Emic is the account insiders give of what they are doing. Etic is the outside analyst’s account. A full answer usually needs both, and they do not always agree.
Relativism has a limit, and it is a real one. Cultural relativism is a method for understanding, not a rule that every practice is equally good. Anthropologists separate methodological relativism — suspend the verdict while you learn — from moral relativism, which would forbid the verdict forever. The American Anthropological Association declined to endorse the draft Universal Declaration of Human Rights in 1947 on relativist grounds, then adopted its own Declaration on Anthropology and Human Rights in 1999. Working out why a practice makes sense to the people who do it, and deciding whether it harms anyone, are two different operations. Lens ② is the first one. It does not excuse you from the second.