I think that there are several major problems with Harrison's argument, the most important of which is best summed up by one of his own subtitles: “It's all Down Here in Black & White”. That is, he makes the assumption that worldbuilding need exist in a strict binary, wherein a setting is either constructed in encyclopedic detail or exists only as a paper-thin shell molded to the narrative. In doing so he ignores, as Evan has already pointed out, a potentially rich middle ground.
Now obviously, narrative is king. In fact, the submission page for this Tumblr informs us that it, “does not include worldbuilding for its own sake; that is, without storytelling being of central importance.” Lots of people use encyclopedias (or, they did, until Wikipedia rendered them more or less obsolete), but you'll find remarkably few people willing to read one cover-to-cover. There's a reason for that: the format is useful in certain contexts, but consuming it in its entirety is unlikely to entertain or educate anyone. This, more or less, seems to be the point that Harrison is trying to make in his first few paragraphs: when he makes the claim that “worldbuilding is dull,” what he is really deriding (I think) is the info dump. In particular of information that overrides the reader's ability to imagine things like a place's history or a physical appearance without contributing to the narrative in any meaningful way.
This is all well and good, because nine times out of ten this sort of info dumping is a component of bad writing. Unfortunately, Harrison insists on conflating the two things, falsely constructing this bad writing habit as an intrinsic component of all worldbuilding. This assumption that worldbuilding on the part of the writer must out of necessity lead to every bit of that world being explained to the reader is patently false. In practice, the information developed during this process should only be conveyed to the reader where relevant, whether thematically or to the development of plot or character. The remainder should exist primarily in the writer's notes, to give context to his or her own thoughts or be used in relevant side-stories, spin-offs, or the occasional Tolkien-esque appendix (or setting-related wiki, the equivalent for the modern online publisher). For the reader, an extensively world-built setting and the sort of fiction Harrison advocates, when both are well-written, may very well be indistinguishable.
The other major problem I have with Harrison's article is that despite his claim that he is referring to, “immersive fiction, in any medium,” it remains clear that his primary concern is for prose -- which is only one medium for which extensive worldbuilding is undertaken, out of many. The majority of these mediums are visual, and thus intrinsically representational in a way that prose is not. Comics, video games, animation, film – all of these require different contributions from their creators and readers/viewers/players. Angela Melick says in her response that, “You can convey so much more about a setting and world through drawings that you might not be able to through text.” I would take that statement one step further, and say that any story told in a visual medium requires that its creator convey information easily withheld in prose, whether that information is a landscape, or a character's body language – a necessity counterbalanced by the fact that it is much easier to convey that information without causing the narrative to drag (through showing, rather than telling, naturally).
Now, bear in mind that this next bit is very much my own conception of things, and obviously the specifics vary from medium to medium, but I would propose that when telling a story in a visual medium an artist has two primary options (with a whole spectrum between, of course): that is, the visuals that an artist produces can be either purposefully sparse, or densely packed with information. The first option is a method of conveying information where what you don't see is just as important in creating a sense of place as what you do see, and a great deal is left up to interpretation. This approach strikes me as being more common to film and in particular video games (where the requirements of good gameplay tend to eliminate unnecessary visual information as clutter). For example, take the film Dark City, or the games Shadow of the Colossus and SMT: Nocturne. In my mind, this is the closest a visual medium can come to what Harrison proposes is the 'right' way to tell a story.
Now the second option, I think, merits further division. Those stories utilizing densely-packed images fall into two further categories: those packed with meaningful information and those packed with meaningless information. The first category is where worldbuilding is most useful. Here a scene is created after the artist has considered its elements in advance. Creating a city scene? Well, what is the architecture like? What kind of people live there? What does their writing look like? This sort of prior consideration can help to create a more visually consistent, 'realistic' setting. Although Harrison would probably deride any intention to cast an invented setting as 'realistic', doing so can, in my opinion and my experience as a reader, help to reinforce suspension of disbelief, and to prevent a narrative from sagging while one wonders why, expanding on the city example above, every building looks like the result of a different architectural era, or why each street sign seems to use a different alphabet. It can also be used to draw an inquisitive reader's attention in a desired direction: let's steal Angela Melick's example and say that everyone in your setting's culture has a specific tattoo, and at some point, this is going to be an important plot point. Prominently displaying that tattoo on all characters of the appropriate culture can pique your reader's interest and serve as a nifty piece of foreshadowing, so that when that plot point arises your reader will already be interested in that particular point.
In perception this meaningful information approach is more often associated with stories that take themselves slightly more seriously, or have something to say beyond the obvious narrative. Conversely, I see the meaningless information option as being more frequently utilized in light-hearted, carefree works, or entertainment that exists purely for commercial purposes/entertainment's sake. Adventure Time and Katamari Damacy spring to mind, in that both are very visually rich, but there isn't a great deal of worldbuilding embedded in those visuals. We could ask why the King of All Cosmos dress the way he does, but ultimately there is no other answer than 'because the developers thought it was funny'. In this type of work, much of the visual information tends to be made up on the spot. (If anyone can think of a more serious work with this sort of meaningless-information-packed approach, please do let me know.)
I suppose what I am trying to say with this whole breakdown is that worldbuilding is just another tool and technique, and like any other it has its place. For Harrison to say that “worldbuilding is not technically neccessary [sic] ” is, in my mind, equivalent to my saying that breaking the fourth wall, or starting a story in medias res is not technically necessary – use of these techniques is never strictly necessary, but for each there are situations in which they are capable of enhancing or detracting from a narrative (as I have hopefully illustrated to some extent above). The primary difference between these techniques is that the ones I list are visible to the reader/player/viewer, while worldbuilding (as I have said earlier) ideally should not be, except in an oblique sense.
That being said, worldbuilding is a very broad term, and as a technique I think it is capable of contributing positively to a narrative in the majority of situations. Earlier I said that a writer should use worldbuilding to “give context to his or her own thoughts.” Now one of the best pieces of writing advice I ever received was never to place theme before story. Never to decide what a narrative's theme would be before that narrative is written. I like to see worldbuilding as a sort of tool that allows an author to brainstorm this sort of thing – by taking some time to flesh out the areas of your world where your narrative is taking place, you as an author are able to feel out thematic connections and images in a more natural way. Whether it's landscapes and writing systems that serve as visual metaphors, cultural practices that tie into a character's motivations, or simply a way out of the doldrums that catch so many authors between the beginning and end of their story worldbuilding can be a source of valuable ideas that would never have occurred to you independently.
Finally, I think it's worth noting that more or less by his own admission, Harrison is going out of his way to be inflammatory (and I think a little needlessly pedantic). Statements like, “... flatters everyone into illusions of anthropocentric demiurgy which have already brought the real world to the edge of ecological disaster,” hyperbolic and vilifying as they are, indicate his intent to provoke and suggest it in the rest of his writing. Being an apparently intelligent and educated person, he is probably acutely aware, for example, of his omission of any sort of middle-ground between what he calls “worldbuilding” and “writing”, and likely intended it to be as much a method of provocation as his imagining of “the great clomping foot of nerdism.” In the end, I'm not entirely sure that this article was meant to advance the conversation in any meaningful way than it was meant to drum up some controversy (and thus publicity for Harrison).
To sum up, I guess I would say that I don't think this issue can be boiled down the X-technique-is-better-than-Y-technique statement that makes up Harrison's article. I think it's really a matter of sizing up your core narrative as a writer and an artist, and then selecting what you think are the most appropriate tools for the job, and remembering that the best and last rule of storytelling is that ultimately there are no rules so absolute they can't be properly bent or broken.
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