You make a good point, OP, although for what it's worth, Lauren Faust herself approved of at least one piece of humanized fanart.

@Short Circuit
The point is, there's a difference between liking something in the fandom, and liking something in the show.
Some things are better as imaginative make-believe, just because I love seeing ponies drawn as humans doesn't mean I think it's a good idea for that to happen in the show.
Fan content isn't permanent. If someone draws Twilight battling Celestia, it doesn't become a part of the canon, and therefor we can do things and explore situations that can't or shouldn't actually happen. Fallout: Equestria, would be another example.