I have read parts of Malory.
But for some reason, the possible reality of the Arthurian legend fascinated me. I don't mean the feminist-druid stuff which I think is stupid; I mean, the real Dark Ages stuff with that wacky monk, Gildas proclaiming doom all over the place only nobody is listening, and there's all these Saxons moving in and, really, there probably weren't any major wars, just a few skirmishes, and it's very possible that the skirmishes were the Celts fighting each other, NOT fighting the Saxons. Because the Romans have left by this point, so the Saxons basically have free-loader rights to that "green and scepter'd isle." And boy, I just love that stuff.
(Now that I think about it, it's books which use parts of the Arthurian myth to create a separate fantasy that I like--like Susan Cooper's Dark Is Rising series. And C.S. Lewis.)
Then, as an undergraduate, I developed a real liking for the other (older) Arthurian legends: Gawain and the Green Knight and Gawain and the Loathly Lady (Wife of Bath stuff).
But of course, if you read anything about King Arthur (or Artos) or the Round Table, you are going to run into Galahad and Monty Python and the grail and Launcelot.
I developed a distaste for Launcelot early on. It isn't just that he has an affair with Guinevere; it's that he whines about it. The whole Lady of Shalott fiasco is Launcelot feeling sorry for himself all over the place. He forgets who he is and falls in love with this other chick (the Lady) and then remembers who he is and decides to go back to the (married) woman, Guinevere, and then the Lady kills herself and instead of Launcelot saying, "Them's the breaks" or "Boy, I was a jerk," he gets all mopey and goes off to try to redeem himself and really, it is exactly like Leonardo on the Titanic and you, the audience, wishing desperately that Billy Zane would shoot him.
I much prefer Mordred. And interestingly enough, I'm not alone. A lot of YA books have been written in favor of Mordred or from Mordred's point of view: the Book of Mordred by Vivian Vande Velde; The Winter Prince by Elizabeth Wein, for example.
I think there are two reasons Mordred fascinates us Mordredites:
(1) Mordred is much more ambiguous than any of the other Camelot/Arthurian legend characters. And he is placed, plot-wise, in the position of being the character who outs the well-liked but corrupt "good" guys.
Basically, Mordred is Spike.
And ambiguity is interesting. I think it is no error of human nature that the most popular Star Trek characters are those characters who are struggling to define themselves: Data, Seven of Nine, the Doctor. (House from House.) We are more interested in people who haven't figure themselves out completely yet than people who have because most of us fall into category one rather than category two.
(2) If you root for Mordred, you inevitably don't root (that much) for Launcelot, and Launcelot is such a great guy to hate. Launcelot is the quintessential spoiled kid who goes off to college or prep school or wherever and gets into trouble with some other spoiled kids. He may even be the ringleader, but it will never be clear; he will never own responsibility. And then they all get into trouble, and the other kids may even get expelled, but Launcelot goes and cries and says how SORRY he is and how he never meant it to get out of hand and isn't it too awful and it wouldn't have gone so badly if it hadn't been for that other guy (who told on them).
I've written two Mordred stories myself. In both, he is not dissimilar to Vivian Vande Velde's portrayal of Mordred as extremely tight-lipped. (My Mordred is less heroic.) If I remember correctly, Wein's Mordred is seriously dysfunctional and kidnaps his half-brother. But he is still the protagonist.
So reason #3 for being a Mordredite must be: he supplies so much great material!