No, I’m not writing it, but I’m not knocking it, either!
I know a lot of people do look down on fan fiction, mostly because it traditionally hasn’t been the best quality. In fact, back in the old days, when I first was trying my hand at writing, it was very much denigrated and no one really wanted to admit that they wrote “fan fic”. It was, after all, problematic in a number of ways. For one thing, it was never going to get published. No one who’d created a fictional world was ever going to let someone write in it, uninvited, and then make money from the effort. Even if authors were okay with it, publishers wouldn’t be. Secondly, it was difficult to share with fellow fans. This was back before the internet, after all, and we had to exchange it all in person at conventions.
But, things have changed.
For one thing, there is the internet now. And, you can write and share your fan fiction on many sites, like FanFiction.net. For another, with some small tweaks which are easily accomplished via today’s modern word-processing software, your work might actually be publishable. Don’t think so? Well, the Fifty Shades of Grey trilogy started out as Twilight fanfic. But, with some name changes, it was converted into something salable. (I’ll let you form your own opinion about quality!)
And, fanfic is even more legitimized by Amazon’s Kindle Worlds service, which lets you write in one of their licensed worlds, for publication. And, those licensed worlds include some relatively big-name settings, like G.I. Joe., Veronica Mars, and The Vampire Diaries.
So, if you still have stories in you after last month’s NaNoWriMo effort, even if they are drawn from your favorite commercial setting, you should go ahead and write them!