Fine fine, I was a bit sloppy. So let's go back to the original argument.
You asked why something like that exists. Well, someone made it. Yes it's shock value, guro and all that. But that's what the guy does, people buy it and clearly "based on a true story" does add an extra edge to it. So isn't it working as intended? The fact that it works and finds an audience is all it really needs to explain why it gets made.
So if you question why it exists maybe you should ask yourself what strong reasons there exist in a free society that would prevent it from existing. I.e. why not?