For me it's not so much about whether or not it's legal, but just about the vibe of the site in general. Tapas is already on thin ice for me, because I just don't feel like I, as a story teller, really fit in with the types of stories that are read. The diversity of readership on this site already tends to have somewhat tunnel vision in what they want to read, and what those things should be drawn like, despite Tapas trying out different things to try and get them to branch out.
I don't have a problem with fanfic, and I don't consider it a lesser artform or anything, especially since a bunch of adults write it so that they can get real deal jobs writing for TV (I have a friend who is a film major and this is just what she does). And, a lot of illustrators write it to get jobs (if you want to work at Marvel, write short marvel comics for your portfolio.)
BUT, what fanfic does do is perpetuate certain very niche audiences that are only looking for one thing in one style. Most fanfic doesn't encourage reaching out of the box and have a lot of inside jokes that assume you already know the fandom. Not even if you know the show--but the fandom of the show. It's like the niche of the niche. A fun place to hang out, but not something I'd want to commit to long term. Like once upon a time I was super into Harry Potter, but then I grew up. Do I read or remember those fics anymore? Nope. Fanfic audiences are very flash-in-the-pan here one second, gone the next.
But what I do appreciate about Tapas, and what brought me here in the first place, is their encouragement to make original works. I actually came here because of the comic, Terror Terror Terror, because it was so freakin weird and original. I want things to stay weird around here, and that can only be done by encouraging things that are new and different.
Fanart again, it's fine, I make a lot of it when I want a cozy, comfortable place, but...when you're doing it for views it becomes such a job. So, in all, I think fanart on this site is fine, but yes, it shouldn't be on the front page--we should continue to encourage original stuff because the readers looking for the niche fanstuff already know where to find it. It's the originals that need the leg up.