1. Sex safety ed needs to be taught, otherwise you get STDs and pregnancies. A couple of hour lecture in school is not enough. Safe sex practices is something that has to be reinforced and encouraged.
2. Respect of consent (and situations where consent cannot happen no matter what either party says) and understanding how to properly express yourself to the opposite sex is extremely important. Our society is full of people who do not treat the opposite gender fairly and do not understand the importance of enthusiastic consent in intimacy.
3. Normalizing sex positive attitude. Many people feel shame from sex/shame others for sexual behavior/repress their own natural desires/etc, this needs to be counterbalanced, especially in a puritanically perverted society like the US.
"Almost nude" simply means not nude, and personal, private nudity is obviously different from seeing other people nude.
Even if someone doesn't mind seeing naked people in the situations you describe, it still doesn't follow they should therefore be okay with nudity on screen in front of their family.