One problem with fiction is that we often simplify complex characters into narrow stereotypes. A common stereotype is the dichotomy between the "virtuous" Madonna and the "impure" whore. Females who fail to live up to the Madonna standard must be a Whore; driven exclusively by sexual desire and lacking in morality/humanity. Pretty much anything can cause the "fall" from Madonna, though it is usually connected to something sexual.
Sandbox / Madonna–Whore Complex