That is exactly what happens in rape trials, though.
The victim's past is dragged up, going back years. The number of sexual partners, emotional stability, medical history, criminal record, relationship with friends and family, photos that show the victim partying (beware what you put on the internet) - everything.
It is sometimes said that the trial is as bad as the rape for the victim.
Physical injuries don't necessarily prove a rape. Some people enjoy rough sex, or they could have fought after consensual intercourse.