A couple more, from ‘70s movies I saw just from the past couple of days, then I’ll leave this alone:
In Animal House, Larry gets drunk with and fools around with the supermarket checkout girl/mayor’s daughter. We see her bare breasts and there’s the famous devil/angel scene on his shoulders. Later before they’re about to “do it” on the football field, she says she has a secret: she’s only 13. The movie doesn’t show anything, but in a later scene, they approach her father the mayor and declare that they’ll have to get married.
In Arthur, the hooker at the beginning of the movie reveals that she became one in part because her father raped her when she was 12. This is a comedy, of course, so Arthur cracks jokes about this. They later have sex, he pays her to leave, then they move on to the next scene.
If you were to immerse yourself in enough entertainment from the early 1970s-early 1980s period, you would inadvertently stumble across hundreds of examples of this kind of imagery. It was just a weird detour from basic decency in our cultural history.