Bear in mind also, Jason, that the skill/craft/art that we call 'writing' is a misnomer - as many wise authors have observed, it should be called 'rewriting', because that's where the real skill lies.
Creating an engaging work of fiction and then polishing it into a potentially publishable work are two sides of the one coin. The first draft is (ideally, for most writers, it seems) the phase where you allow your creative urges to run riot and create something fresh and original, with only minor regard for grammatical accuracy and overall coherence. Quite a few writers are able to do this successfully.
It's the second phase where most fall down. Subsequent passes of your ms are where you fix the lapses of grammar, point-of-view issues, pace, consistency, plausible characterisation, plot backfilling and setup, superfluous-character elimination and the like - the myriad things you have to get right to make your work hang together as a whole. This is where the succesful writer has to don an editor's hat and ruthlessly weed out everything that doesn't belong and/or replace passages to make them work better.
This is a hard-won skill, and only (typically) comes after a few false starts. It's often said that you have to write a million words of crap before the good stuff emerges, and most successful writers confirm that this is the case. It's not the originality of thought and creation that's lacking, but more the developed critical faculties that enable you to recognise crap, because it stinketh and doesn't belong in your otherwise fragrant ms.
Those who can't be bothered to learn this skill are the ones that point to the publishing sucess of sub-literate scrawlers whose work was fixed up by their agent or publisher to make it printable, or to certain well-known writers whose spelling and punctuation are legendarily appalling. But those exceptions do not prove a rule. The only reason they get away with it is because, as UJ frequently points out, "story trumps everything". Writers who are so good (or have established a reputation as a best seller) that they don't need to worry about these things are extremely thin on the ground.
Professional editors (evil or otherwise) exist not to fix stuff you should have done yourself, but to cooperatively make something that's basically good even better. They are, effectively, a qualified resource of second opinion - like one doctor to another. It's not a doctor/ill-informed patient relationship.