Comparing fanfic to original writing is not quite like apples and oranges. It’s more like grapefruit to tangelos. Okay, so fanfic is writing – but it has a different purpose than original writing, and to urge fanficcers to stop wasting their time and write something original ignores that the act of writing is almost incidental. (Yes, yes, you who are about to object, you’re precious, creative stars in the galaxy of craft. Just a sec.) How I communicate to a reader as a writer is drastically different in purpose from how fanficcers communicate with other fandom folk. Yes, they have a lot in common – but the primary purpose is different, the human motivations are different, and that changes everything.
Go read the whole thing. It’s chewy crunchy thoughtfood.