What about writing about the necessity of myths? Ancient peoples such as the Greeks and the Romans felt the need for explaining the different phenomena of their world, so they created an intricate mythology that is still studied and alluded to today.
In the modern world, there is yet a need for myths, something to believe in that is greater than we are. Such novels as F. Scott Fitzgerald's The Great Gatsby and John Steinbeck's Of Mice and Men, for instance, illustrate the need that men have for the myth of "The American Dream" and for the dream of the ranch, respectively.
Why don't you write about a certain type of myth? For example, you could discuss the various myths that exist in many cultures that explain the rising and setting of the sun. You could examine American Indian myths regarding the sun and moon as well as ancient myths regarding these celestial bodies (Aztecs, Incas, etc.) Or, you could discuss the similarities and differences in creation myths (how the world was created) or myths about the great world-wide flood that exist in many cultures. You could write about the different myths that explain how evil came into the world (i.e. Pandora's box, etc.) or how man obtained fire or how the world will end. There are all sorts of possibilities. You could also compare Roman and Greek myths. This would be easy because the Romans borrowed a lot of myths, gods and goddesses from the Greeks and just renamed them. This might be easier to do since they are readily available and well-known if you do a little research.