Why should I be afraid?

Knowing what Mary Sue is, the true question ought to be, "Why shouldn't I be afraid?" But, if you really must know, I will attempt to explain the fear.

Imagine that you met someone in Real Life™ who was constantly upstaging you. Someone who, no matter the situation, could never fail. This isn't the parental kind of "I'm always right" syndrome; this is the gloating, superior, negating kind of perfection that grates on your nerves because you, as a human, have flaws.

Mary Sue writing is so idealized, and so chocked full of its author's desires, that it is hard for many others to stomach. Almost all of the time, you don't know - nor do you care - about the author and said desires. Having their wishes fulfilled cannot give you any satisfaction. What's more, you are likely reading the story because you have some involvment in the fandom; when you begin to see characters of whom you have never heard, interacting unnaturally easily with canon characters, you are likely to become either irritated, or suspicious, or a deadly, uncomfortable combination of both. Mary Sue cannot, in the end, make anyone but the author happy. Unless, of course, you can place yourself alongside the Sue, and turn her wish-fulfillment into yours. This is why Mary Sue stories, no matter how odious, are guaranteed to get at least one raving review.

Along with this wish-fulfillment comes, more often than not, very raw, unskilled, unedited writing. It is not unedited in the content sense, obviously. It is unedited in the blatant lack of proofreading sense, including nonexistent grammar and poor spelling. Unconsciously, people are more compelled to reread and appreciate stories that look good and can visually prove that the author took the time to make it pleasant on the eyes. This can be everything from spell and grammar checking to ensuring that the font is easy to read and that the page layout gives you the simplest access to the story. When the author cares about the story, you are more likely to care about the story. By "care about the story," I do not mean that the author will defend it when criticized. This means that the author is genuinely proud of her (or his) work, and can accept criticism gracefully because s/he believes the ideas stated within it.

Belief is the next part of this explanation. A good story is, despite any degree of strangeness or unusual plot, believable. For example, you may not have ever considered something that occurs in a story, but it makes sense to you on some level. Mary Sues do not have this quality (for the most part - there is, perhaps, the rare Sue that manages to make herself believable, but that does not make her any better for it). The plot is often poorly executed, and her presence is due to some unlikely twist of fate. See the "What is a Mary Sue?" section for more on the plot of a Mary Sue. This plot, if one could call it that, is usually so unbelievable as to make readers roll eyes, arch eyebrows, or begin to question things - and not in the positive sense.

This brings me to my next point: the changes, regularly drastic, that befall canon characters in the Sue's presence. In a Mary Sue story, the jaded, bitter men become open and kind, the cheerful characters become more so, and any interruptions to the Sue's "plot" are removed. In the latter case, canon love interests are taken out entirely or are bashed badly, characterized beyond recognition. In the case of the Sue's object of affections, kindness and loveability will either be intrinsic, or will reveal themselves. The Mary Sue, no matter how much the real character would hate her or distrust her, wins everyone's heart - that is, everyone of importance to the plot or to the author - in the end. She can make characters go weak in the knees, give them strange speech patterns (sometimes making nearly mute characters become Tolkien-esque in their descriptive speeches), and bring them to tears. She can spur the cowards into battle, reform the villains - or at least make them think - and encourage some characters to die, be it for the love of her (in some protective moment) or from a plot device designed to destroy an obstacle.

If you truly love your fandom, how can you bear to see this harm inflicted upon the characters you have come to know and love - or hate?