It's true that there are many interpretations of all kinds of books which do not reflect the author's intentions. Doing this is fine so long as you evaluate these interpretations to see whether they are based on reality or not. The main point of books is to challenge you to think about different topics, and validating or dismissing our own interpretations of a text without thinking about them defies the point of reading.

If we do, however, want to get a better picture of a writer's intentions, historical, philosophical and social context are paramount. Understanding the beliefs of the author and the context within which he/she writes is the only way to get an idea of what their intentions are.