During a recent re-watch of this movie, I realized that everyone still refers to Lecter as "Doctor". This is a minor point, but wouldn't he have been stripped of any such titles once the news got out that he'd been, you know, eating people? I can understand Starling and Crawford referring to him as such, but Chilton even introduces him to Senator Martin as "Doctor Hannibal Lecter". You just know that he'd be the first one to stop using the title if it weren't necessary. So what gives?
I see it as a subtle commentary on Lecter's character. He has done things so heinous and ruthless that just hearing about them would make you squirm, yet he is undeniably brilliant and even the FBI still has a great deal of respect for him. It's also interesting given the character of Clarice, who is portrayed as sort of a timid but brave interloper in an otherwise male-dominated law enforcement world; perhaps the connotation of "Doctor" also serves to juxtapose her disrespected FBI character against a well-respected cannibal. It's also a constant reminder of the duality of his role in society prior to his capture, and there is a sadistic subtext in the characters referring to the psychotic madman as "Doctor." So I'd say half of it is purely to serve the script and the other half is the characters acknowledging his intellect (especially since much of the movie revolves around them trying to get information and assistance from him).
It's also a way of distancing themselves from him, to keep their conversations as impersonal and formal as possible. They'll call him "Lecter" when he's not present, but when he's actually in the room with them, "Doctor" is a better option, giving away less about their feelings towards him than using his name might.
As long as there was nothing wrong with his thesis, I don't think they can.
Even if his license to practice psychiatry has been revoked, he's still entitled to the honorific.
Chilton introduced him as "Doctor Hannibal Lecter" because he wanted the introduction to be more dramatic. Same goes for the little flourish of his hand. In the novel this is when Senator Martin beings to realize that siding with Chilton was a mistake.
In the novel, Dr. Lecter still writes articles for medical journals while incarcerated.
HOW did Lecter get that pen??? In the film, at least, it seems like the only way he could possibly have grabbed it would be if he used the Force. Which, ya know, is totally legit.
Chilton was careless one day and left it in his cell. This is thoroughly explained in the novel.