Is Harry A Horcrux? Part II

Is Harry A Horcrux? What clues has J.K. Rowling herself dropped? Snape: Villain, hero or something else? Who dies in Book 7? Ralph Fiennes -- born to play Lupin, not Voldemort? If you're interested in those topics, see previous posts, below.

(And let me just say that I'm fascinated by the theory (see comments in previous post) that it's Harry's scar that's the Horcrux, and all he has to do is get rid of his scar. So a bit of dermabrasion would save the world from evil!)

Earlier today I promised a longer look at why some folks think there's no way Harry could be one of the missing Horcruxes. Here's one person's semi-rant:

Do I think that Dumbledore was right and Voldemort intended to make a Horcrux with Harry's murder? Yes. Do I think it's possible to make a Horcrux accidentally? No. And if Harry was a Horcrux, it would certainly be accidental.

On page 498 of the American edition, Professor Slughorn says to Tom Riddle, "There is a spell [used to encase the split portion of the soul], do not ask me, I don't know!" Now, it follows logically that to create a Horcrux, one would commit murder, then take the desired object and perform the incantation. And, presto, you have your Horcrux. Meaning that (a) it can only happen on purpose, (b) it can only happen after the murder has taken place and (c) it sure as hell didn't happen to Harry the night his parents were killed.

On top of that, it just doesn't make any sense to me.