I am not a teen.
The fact that you only equate sex/nudity to porn reveals the problem.
I took the trouble to delineate tasteful nudity, or sex that actually serves a purpose in the plot (your fine examples of drama or fear are great suggestions, though I worry about the encroachment of porn with a “fun sex scene”) from common smut.
As for public life: the theater is a public place, my thought goes no further than that.
Thinking back now, I can even empathize with some of your feelings here. In the abu dhabi branch of the louvre, there is an ancient marble statue of a man that stands twice my height if my memory serves. Its genitals have been roughly gouged out with chisels in stark contrast to the smooth curve of skin and cloth for the entire rest of the statue. It’s nauseating and disrespectful not just to the creator’s work and vision but to human dignity. I think me seeing that statue and feeling what I felt is something comparable to how you now feel. I’m not afraid of or ashamed of the human form or human sexuality, but these things have a time and a place and a respect due that is often not granted or even considered.
So maybe im just watching the wrong movies. what not-porn movie are you watching that treats sex with the dignity and respect it deserves?