I dissagree that social nudity or any kind of general nudity is porn.

I agree that "non-graphic representations of sexual intercourse or masturbation" or any thing that suggests sexual activity is porn.

For me the definition of what constitues porn is not... that it induces sexual arousal.
As suggested in several posts... lots of things can induce sexual arousal that are not specifically sexual in nature.
Underwear catalogues may be designed to induce sexual arousal because the girls are all slim and pretty and posing in sensual manner. I don't see this a porn.

In my view porn shows or hints at sexual activity.... it may or may not induce sexual arousal. Like, if I looked at a vid of two adult females having hardcore sex it would not arouse me... but it would still be porn.

Nudity.... especially social nudity.... does not hint of sexual activity and is therefore not porn. I may be arroused by the sight of a naked person.... one could even sit and masturbate to such an image... but that would not make it porn. In that senario the porn would be happening in the masturbating person's mind where they are imagining sexual activity with the naked person.

I also disagree with the idea that all sexual arousal is lust.
Lust is a hunger to actually HAVE illicit sexual activity.
Desire for it... with no intent to ACTUALLY pursue said activity in the real world... is not lust.
EG: I strongly desire sexual activity with a boy. I may even see a good looking boy in particular and strongly desire sexual activity with HIM. I may even get arroused by the idea of it. So far this is NOT lust.... it is only desire and arousal.
If I take that desire and then MOVE ON to thinking: "How can I get this activity to happen?" then I'm lusting. As soon as I begin to act or seek out or make plans to act on my desire then I'm lusting.
If I say... opps this desire's not helpful... it may lead me to lusting for this kid... so I go away and have a tug to disarm the heat of the desire... then I'm taking responsibility for my sexual desire and moving AWAY from lust.

I agree that the arousal/lust issues are moral issues and have nothing to do with what makes something porn.

Blessings
Cat.