Where do Fandom and Cults Differentiate Themselves from Each Other?

The almost insane curiosity that science fiction and fantasy fandom direct at their favorite books, movies, television shows, and radio dramas (or comic books, art, etc.) has been compared more than once with cult-like devotion to religious leaders and icons.  In fact, the word "cult" itself has many meanings, and is related to words like "agriculture", "culture", and "cultivate".
We do appear to worship the Star Wars universe in many ways.  Some fans are so devoted to the Star Wars experience that they meet regularly in costume and ... and, well, do things like the Tolkien fans and the Star Trek fans and the Pern fans and the Hunger Games fans.  And it goes on and on.  Millions of people have identified with the science fiction way of life.