7. No Need To Bring Moriarty Back
Jim Moriarty is dead. He has ceased to be. This is an ex villain (had to get a Monty Python reference in somewhere). As such, there needs to be a very good reason to resurrect this character and sacrifice the believability and legacy of the series. In truth, there is no justifiable reason to do this. Fans of the franchise know that Moriarty dies at Reichenbach and expect this fact to remain unchanged. Furthermore, bringing Moriarty back would shift the core focus of the show away from character based mysteries and would demote one of the best villains of all time to a recurring guest character.