research papers are all about you finding out about something and proving to the person marking your paper that you've actually done your research. They already know what the topic is all about, they're probably the ones who have to teach every year. Rhetorical questions will make your essay sound something like an extended script for a lecture and in some cases make the reader feel as if you think they have no knowledge about the topic. Really, they should only ever be used to argue a point, make the reader think about the situation and force the reader to look through your perspective.
