Without diminishing the horror of sexual assault, and while agreeing that it should be punished severely, it is--after all--just one form of assault.  One could argue that other forms of physical assault involving disfigurement, permanent physical damage, etc. are no less horrible.  The elevated horror with which we view sexual offences is largely a reflection of our society's squeamishness about sex generally.  Investigations of crimes, levels of proof and evidentiary rules should not differ just because of the type or nature of the crime.