It's important to understand that Hannibal Lecter is insane and is trying to reverse the death of his sister Misha. He even tries to build equations that could reverse entropy and thus the the flow of time - these calculations are described as elegant at first but quickly devolving into insanity and wish-fulfillment. He, however, believes he has found a way in Clarice Starling.
This is where the book Hannibal diverges in the extreme from the movie Hannibal:
In the final chapter, Hannibal actually keeps Agent Starling in a childlike state and helps her achieve closure over the death of her father. He uses hypnosis and narcotics, and Starling is unable to fight him and actually partakes in eating Agent Krendler's brain. After this meal, she seduces Hannibal and helps him achieve closure over the death of his sister. She asks him: "Were you ever angry at Misha because she took your mothers breast from you?" to which he replies that he doesn't remember (a probable lie). She offers him her breast and tells him that this one will never be taken from him. He accepts and they find true happiness together.
Something else the movies don't explain very well is the fact that Hannibal has been trained from boyhood in the ancient art of building a memory-palace. This is how he has achieved his photographic memory. After fifty years of practice his palace has such a greatness that he can escape into it and can resist torture by staying in his own mind.
Hannibal has suppressed the memory of eating the broth made from his sister.
However, as one of the characters he murders says: "You have to kill everyone who knows, don't you?" It would appear that he also needs to eat from the men who ate from his sister. Why the habit continues is not explained in the books nor the movies other than for enjoyment and the love of cooking.
In the narrative, he seems to find cannibalism comforting, and remember, he only eats 'the rude'. The men who ate his sister and fed her to him, were war-bitten rude men of low education. I suspect he hunts them still and will never stop. The ending of Hannibal the book is ambiguous and we only know that he shows up in Rio with Starling, and that Barney spots them and flees the country without notifying anyone. This is the terror Hannibal strikes in people. He truly is a monster and seeing him unrestrained is terrifying.
For lack of a better description, I would call him a superhero cannibal. A truly unique entity. The people who get in his way are removed but not necessarily eaten. Again the text is ambiguous. We know of many victims that aren't described very well, such as the curator who held the position he wanted and a student's body that was never recovered. Also, he didn't eat from Mason Verger - apparently he was only good for dog food.
Thus Dr. Lecter seems to have strict standards and appears to uphold them religiously within his own insane frame of reference, which is only vaguely described so far. No one knows if the tale will be continued for such is the mystery of the author, who prefers not to say anything until after the book is written.