"If I saw a little girl or boy being raped, I would make sure to stop it, that is the difference between me and your god". This quote literally changed my life.
I don't think the villain will do it where the act can be seen. If the victim is a little girl or boy, the villain will surely drag the victim unconscious somewhere secluded, in a classroom or maybe inside a vehicle.
But just to go along with the flow: If the rapist is not a lot bigger than me (I'm not even 5'5" ) I will stop the crime by whatever means, regardless if he's holding a knife or even a machete. If he's holding a gun, I'll call for backup.
If there's two or three of them just about my size, I'll take them on even if they have lead pipes or katanas.
If they're a lot bigger than me and they saw me, I'll run for my life and seek help before I get raped myself and get dumped in a trash can with a broken neck and pelvis.
When you get a believer who will admit their doubts, they will tell you that they wonder why their god does things a certain way, allows horrible things, creates horrible things, and that if the believer were god, they would do it differently. But then many of them become frightened and retreat back into cognitive dissonance.