Having read the books (including "Hannibal"), I come to a different conclusion about Dr Lecter. He is neither a psychopath, nor a sociopath, but a form of Nietzsches' 'Overman'. Someone whose experiences, losses and hardships along with his intelligence, has taken him beyond morality and law. The people he kills or cripples are mostly contemptible. Many of his actions - the maiming of a nurse while in prison, for instance - are aimed not at the direct victim, but at someone else. The nurse was attacked simply as a lesson to Dr Chiton not to treat Lecter as an 'ordinary' prisoner. He eats his victims as we eat non-sentient animals, because that is how he regards them.
He sees the same potential in Will Graham and Clarice Starling. Graham fails. Clarice, however, passes every test and, in the end, under his tutelage, herself transcends the society and morality which will always hold her down. She becomes his equal and partner.