Why don't the thuglicans understand the concept of "consent"

Digby writes and interesting post on "consent" in response to this comment on her blog:

I have noticed that "right wingers" have a lot of problems with the idea of consent: they can't tell the difference between Abu Graib and a "fraternity hazing" or bondage-play, between consensual sex and rape, between "torture techniques used on trainees" and "torture techniques used on prisoners".

Does anyone know what their problem is? Has there been any research that sheds light on why they can't wrap their brains around the idea that someone who agrees to have an appendectomy isn't signing on to be disembowled by the next psychopath that comes along?