* Most people who are sexually assaulted know their attacker and are not attacked randomly on the street. This makes self defense scenarios unrealistic, as there is already some level of trust between an attacker and the survivor
* Most sexual assaults will go without arrests and prosecution. There have already been cases where women have been arrested and sent to jail for self defense (CeCe Mcdonald's case comes to mind), including the Marissa Alexander case where someone fired a warning shot at their abuser and was sent to jail: http://en.wikipedia.org/wiki/Angela_Corey#Marissa_Alexander_...
* Sexual assault and rape aren't just about incidents, it is about a culture that supports rapists and demonizes survivors and dismantling that culture is the best way to defeat sexual assault