Rapists can appear to be the nicest of people. They can often be like Dr. Jeckyl and Mr. Hyde. One minute they can be charming, and the next minute, they are forcing sex on you. Rapists force sex on their victims in order to obtain sexual satisfaction. Rape is actually a crime of power and control.
Sex is simply the means of using that power and control over people.
Very often, the victim knows the rapist. Most people think of rape as a total stranger attacking you from behind in the dark and forcing sex on you. Although this may sometimes be the case, very often, the rapist is someone you already know. When the code word is mentioned, this gives the submissive partner control over the situation. Now, if sex continues despite the use of the code word, then this becomes rape.