I am a fan. I have been active in fandom for more than 20 years, and lurking at the edges for more than that. I'm not a "big name fan," and I can't speak for all of fandom, but I can offer my answers.Why would you want to mess with someone else's characters when you can create your own?
Why do kids play with Barbies when they can make their own dolls? Why do you drive a car someone else made, on roads someone else made, when you could be hiking on trails of your own? Why do you watch movies and TV shows--and presumably, talk about them--when you could be making your own? Why do gamers play D&D instead of the game their friends created?
Okay, maybe you don't have the skills to do all those things, and fanfic authors *do* have the ability to write. (Um. The better ones, anyway.) But even directors watch other people's movies. And talk about how they'd've done it differently, or how they liked some part, or how the sets over here could've been different and that would've changed the whole scene.
Fanfiction is exploration of and commentary on
the stories. Like essays in a different format.
About the image:
Snape and Harry were not "modeled on Rikhman and Radcliffe." Have you read the books? Do you know how closely R&R resemble the book's descriptions of Snape and Harry? (Snape is, I believe, thinner than Rickman. Which picture-Snape was.)
I've researched the relevant laws. (1) This picture doesn't qualify as "child pornography," because that would require a real human child
. The fictional character "Harry Potter" is not a person, has no civil or legal rights, and can be killed, tortured, raped, or whatever. (2) In order to involve the laws on "Obscene depictions of minors being abused," the picture would (a) need to depict a child (as you noted, debatable), (2a) be "obscene" by the Miller test (which requires judging it by "community standards"--which DOES NOT mean "these three members of the community found it offensive"... and LJ has repeatedly refused to state which community's standards they'll be using), or (2b) depict graphically (which means "visible genitals," which the pic has) a certain list of sexual or tortuous activities (which it does not).
Legally, LJ had no reason to remove this pic.
Aside from that, LJ's stated policy on Child Pornography--which should be the strictest of their rules--state that f, in Abuse Team member's discretion, there is reasonable suspicion that the poster did not know that the image qualifies as child pornography, suspend the user until the user agrees to remove the images, rather than terminate the journal.
Note that all of fandom has been demanding STANDARDS for months--we DO NOT KNOW which things LJ finds too offensive to host.