Is Fantasy Violence Okay?

Last night I attended the pre-publication launch of Department 19 by Will Hill and got talking to a group of bloggers and publicists. I was busy recommending Long Reach by Peter Cocks - a very fine teen thriller - when one of the people present said that a prominent London bookstore are thinking about removing Long Reach from their teen bookshelves due to the nature of the violence within it.

This rather surprised me. Yes, there is some rather nasty violence in Long Reach - it is a novel about a seventeen year old going undercover within a London gang, with all the threats and murders that this would entail - but I wouldn't deem the violence to be any worse than Department 19, which is gory to the extreme in places.

But then it occurred to me that in the former example people are killing people, whereas in the latter people are killing vampires. Does the fantasy aspect of it make the violence okay? Can we therefore distance ourselves from the blood and nastiness because it isn't a "real" person.

I then wondered about Black Swan - the film about a ballerina descending into madness while she rehearsed a particular role. This film garnered a 15 certificate - but the nature of the horror was, once again, fantasy. She was dreaming her way into horrific situations. If it had been a film about a serial killer with the same horror and tenseness and nasty scenes, would it have received an 18 rating to ensure that young minds weren't terrified?

What is your opinion? Does the fantasy aspect mean that violence and horror is overlooked?