A personal point of view on the necessity of a new culture in fiction
"A long time ago, in a galaxy far far away", "Pandora", "Dune", "Middle Earth". All quite different worlds compared to ours, but every single character (Alien or not) have the common factor of human conflict (which is one of the fundamental cogs of a story). But why we need new worlds? You may say that is the will of the writer, or just a cool feature because the story of a character is what really matters. That's true. But why create, for example, an indigenous culture of 2 meter high blue aliens living in a moon far away from Earth since you have a plethora of these cultures here on Earth (Na'vi people - Avatar)?
Well, maybe one fruitful way to an author decide if he/she needs a new world is to verify if there are "Exotic Culture scenes" on his/her story. The Na'vi people are exotic, the Watto of Tatooine or Yoda are quite fascinating, Hobbits are unusual and so on... But again, there are many "Exotic Cultures" here on Earth. The thing is, are they considered exotic cultures of Earth really exotic? I mean, they are exotic compared to what?
An African Tribe is exotic compared to an every-day life of an average city X of Occidental World? Most people would say aloud: "yes." But if you apply a reference change, a person from African tribe Y would probably say the same about the people of city X. So which culture is really exotic X or Y? If you say that is the city X, you are pre-establishing a "true" culture, which of course do not exist; if you insist without any solid arguments, you may reach the edges of things like racism.
Now, the problem is then to say what is exotic or not. Maybe the creation of a new world and culture (based on Earth but without saying anything related to a particular culture) solves the problem of an "Exotic Culture." Now, in this new world, you can compare all our Terrestrial experience (culture) with something truly different (because it isn't a human feature), truly "exotic."
My question is based on my ignorance about the necessity of a new world. So, beyond genre, why sometimes (mostly in sci-fi and fantasy) we need new worlds to tell about human conflict?