If one adopts the principles of the purity culture, one only reduces the chance of being raped. It should not be portraying itself at 100% effective.
Hang around frat parties, and the chances go up. We, as a society, need to shift our values away from mind-altering substances that cause a loss of judgement and control.
And there’s still too many men who regard women as toys for pleasure — and too many women (who think they are liberated) for playing along. Casual sex, even if consensual, is helping to reinforce the rape culture.