What in hell is an amateur cannibal? ... or a professional one, for that matter?
In the 19th century "amateur" meant connoisseur - someone most familiar with something, yet not depending on it for his or her income. A Regency nobleman could be an amateur of music, meaning he knew more about it than most of the musicians of his day, yet didn't have to earn any meagre wages on the stage; a Victorian officer could be an amateur of boxing, meaning he fought for sport, not for money - even though he could've beaten a fine bunch of prizefighters. Conan Doyle's Sherlock Holmes story
The Dying Detective, for example, has the crook stating of the protagonist he thinks he has poisoned by means of bacteria: "He is an amateur of crime, as I am of disease. For him the villain, for me the microbe." - Now ofcourse nobody would think Holmes an amateur, at least in the field of criminal behaviour, in our sense of the word - no, he's the connoisseur, though not paid by Scotland Yard or any other government funded agency. OK, he does earn his money by making use of his talents and obsessions, but he's not considered to be "a professional" - he's a freelancer in a time when freelancing was rather unusual in law enforcement. An amateur of crime, hence - and I believe De Quincey called himself an amateur of suffering, but I'm not quite sure. He did have a bad headache for the better part of his life, though, so it's a good guess...
