There was an introduction by Harlin Anderson in Dan Simmon's collection
Prayers to Broken Stones that has always stuck with me since I first read it 20 years ago, and I've been thinking of it while reading this thread-- I've finally gone back and found the quote that most applies:
"Understand: I do not believe "anyone can write." That is to say, anyone can slap together words in some coherent sequence if s/he had done even a modicum of reading, and has at least a bare grasp of how to use language. Which is talent enough for writing letters, or doctoral theses, or amusing oneself with "creative endeavors." But to be a writer—not an "author" like such ongoing tragedies as Judith Krantz, Eric Segal, V.C. Andrews, Sidney Sheldon, and hordes of others I leave to you to name—one must hear the music. I cannot explicate it better than that. One need only hear the music. The syntax may be spavined, the spelling dyslectic, the subject matter dyspeptic. But you can tell there has been a writer at work. It fills the page, that music, however halting and rife with improper choices. And only amateurs or the counterproductively soft-hearted think it should be otherwise.
When I am hired to ramrod a workshop, I take it as my bond to be absolutely honest about the work. I may personally feel compassion for someone struggling toward the dream of being a writer, who doesn't hear the music, but if I were to take the easy way out, merely to avoid "hurting someone's feelings"—not the least of which are my own, because nobody likes to be thought of as an insensitive monster—I would be betraying my craft, as well as my employers. As well as the best interests of the students themselves. Lying to someone who, in my opinion (which can certainly be wrong, even as yours), doesn't have the stuff, is mendacious in the extreme. It is cowardly, not merely dishonest. Flannery O'Connor once said, "Everywhere I go I'm asked if I think the university stifles writers. My opinion is that they don't stifle enough of them. There's many a bestseller that could have been prevented by a good teacher."
Similarly, I take it as my chore to discourage as many "aspiring authors" as I possibly can."
So, the reason I'm so anti-"open slushpile" is because I think that good publishers should be not only a promoter of good writers but also a preventer of bad ones.
(This coming from a former aspiring writer who long ago realized that my love of reading did not equal a talent for writing.)