Are we wrong about what religion says is dirty?

If there’s one thing religion is good at it’s defining what’s good and bad, right and wrong, clean and dirty. Whether it’s music, movies, books, or people, dirty things are to be avoided. But religion is just structures created by people who are trying to know and follow God. How can we be certain those structures are right? How can we be sure that what religion says is dirty really is? And how can we know that our lives are actually clean?