If there is some sort of hate, it's probably for the sake of irony. This... girl... kills by slicing her opponents apart without conscious thought or mercy. Even if her opponents are defenseless. (or were just disarmed)
I'll be honest, I remember little of Busou Renkin. I just recall some early scene where she sliced this vampire/etc dude on the ground. I think he was protecting the secret/whereabouts/details of his kin from her, and tried to attack her(unlikely it was to kill, knowing his situation), and she ended him there and then.
In a common world, this would be perfectly excusable. But in Busou Renkin, they make her out to be a good guy.