I know I shouldn't but in, but can't help myself.
It's perfectly possible that someone plays golf just for the exercise value. For that person, exercise would be the primary function of golf. So while golf, in general, isn't exercise per se, it's possible to play golf for exercise per se.
Similarly, while all porn certainly isn't art per se, it's perfectly conceivable that someone could create pornographic material with the intention to create art. So while all porn isn't, it's still possible for some porn to be art per se.