The difference is huge, but not always apparent.
From the perspective of a viewer it can be muddled and to be frank anything that explores sexuality can be pornography for some, National Georgaphic magazine springs to mind.
But see it from a design perspective, im currently working on a documentary.
In it ive filmed several interviews that im mixing with other shots, every shot was carefully considered, every angle was thought through.
Now im editing, and when i transition from one shot to another ive got many choices, fade to black then in, blur them together, barndoor effects, flash transition...
The options are many and I consider each one carefully, i test them, i look at what effect they would have on the mood of the documentary, even though we are talking about one second, something that is sure to pass most viewers completly by.
But as a creator Im creating something specific, and thats the difference, Porn is porn because its designed to be porn, even looking and a dressed woman in a porn film is meant to turn u on, by the angles, the look she is giving, the type of light they use, the type of clothes she weares.
So in my opinion its about design first and foremost.