Just because an image might be considered distasteful to some people it should not be automatically made illegal for someone to create or possess it. If you do this what you are effectively doing is making it illegal for someone to put their thoughts down on paper. It is difficult to understand quite how those drafting these laws fail to realise how close they are getting to the cliched thought police here.
There is no justification for making an image illegal just because the act it shows, if replicated with real people, would be illegal. If you want to go down that route then anything depicting illegal activity should be banned which would require vast numbers of books, films, computer games and songs to be banned.
Imagine for a moment having no experience human culture or morals which come from it and try to understand this.
Murdering someone is illegal.
Drawing an image of someone committing murder is legal.
Sexually abusing a minor is illegal.
Drawing an image of a minor being sexually abused is illegal.
Engaging in consensual BDSM with potential genital injury is legal (last I heard)
Pictures of the above are illegal (in certain circumstances).
A bit confusing isn't it? How about some consistency here? Don't try and pick and choose types of images to make illegal. Just make them all legal and get the police and courts to focus on the people that are committing the real crimes and leave peoples' fantasies alone.
For the record (since someone is bound to bring it up) I condemn child abuse. It is a massive problem but the methods by which the previous government and the tabloid media have trying to stop it (or in the latter case, sell more newspapers without giving a damn about the consequences) is, in my opinion, completely wrong and actually counter productive. Revoking civil liberties, forcing potential pedophiles to bottle up these urges by a combination of making all their outlets illegal and ruining their life if they even try to talk to someone about, and teaching children to distrust adults outside the family (most abusers are from inside the family remember) is hardly going to be successful. But that's for a different article.