I thought it was a good question. Not wanting to be subject to such imagery is not a sign of wrong-headedness, over-sensitivity, or even weakness. It just shows the person knows themself and their limits and there's nothing wrong with that. I'll go with Xar, it's a good idea to ask the author.
It's more likely that people stop reading not because they reason that such a vile character is not worthy of their readership, but because reading about a rape offends their sense of morality. Some people seem to think that by reading a rape in a fiction book they are somehow responsible for a rape taking place, and this makes them feel guilty and they stop reading it.
I'd question that. Judging from reaction here and my own feelings, I'd say people stop reading 1) because they strongly dislike the character and want nothing to do with him (not an unreasonable reaction, and one that people often seem to have in real life to ciminals) and 2) it is too disturbing to continue, just as some movies, like Schindler's List or The Passion are too disturbing for some. I doubt anyone feels "responsible" for any of the things they read or see in fiction, though I would
hope a rape, murder, or other heinously wrong act would offend anyone's sense of morality, whether or not they kept reading a book or watching a movie.