I don't think there is anything wrong with 'pure fantasy' when it comes to music though. Some artists are trying to create an image/atmosphere about being in a particular scenario, why is that any different to film or books? Do they all have to be from personal experience for us to appreciate them?
I don't think there's anything in general that's wrong with creating a fantasy scenario in any form of art. In narrative forms, however, fantasies about the actions of the protagonist(s) by their nature invite audience identification in a way that documentary forms don't.
When you read Conan the Barbarian you imagine screwing chicks in chainmail and hacking the heads off temple guards.
So I suppose I worry to some extent about what you imagine when you listen to lyrics about anal rape or what have you in Odd Future lyrics. I'm not really a big fan of violence against women.
On the other hand, if you listen to Wu Tang, who I live, there's a fair bit of ethnically slanted murder fantasy in there so I'm not sure the distinction I'm drawing is fair. Might just be that this lot haven't been normalised yet.
I'm reminded of Fur Q's 'Uzi Lover' from the Day Today: