Honestly this discussion also highlights the issue that what's considered inappropriate varies widely and often changes both in terms of prejudice and in terms of context. Most people would agree that an image of a penis entering or inside of a vagina is pornographic unless it's a medical diagram laying out the anatomical and physiological aspects like the one in the anatomy book my otherwise puritanical parents let me read at the age of six. Most people would agree that nudity is sexual except for, again, anatomical diagrams, but also many classical artistic depictions such as paintings and statues. Hand holding isn't generally considered sexual except to some people if the people happen to be of the same sex but not if you come from a culture where hand holding is a normal level of intimacy for non sexual friends. Breasts are for some reason considered sexual in most of the areas heavily colonized by people from the places where lactose tolerance past childhood evolved but not most other places which is super handy if you like being able to feed infants. Most people agree that kissing for an extended period while rubbing areas close to the genitals is sexual, but often not enough to restrict it from being viewed by teenagers.

TLDR; what's even considered "sexual" or "porn" can vary wildly and has historically been used to suppress education, various minorities, and general freedom of expression.