Any idea that is sufficiently different from your current worldview will feel threatening. Therefore, if you want someone to think or change a belief, it is best done in a non-threatening environment.
Debates and arguments are like a full-frontal attack on a person’s identity. People tend to get defensive when engaged in this way.
Books are often a better vehicle for transforming beliefs. With a book, the conversation takes place inside someone’s head and without the risk of being judged.