Is porn always destructive?
I'd argue that anything designed to deliberately arouse sexual desire other than the arousal you experience with your spouse, is destructive. Why? Because it weakens your exclusive sexual bonding/attachment with your marriage partner. And it constitutes a temptation toward fantasy and masturbation, which is to say, a disordered diversion of the sex drive.
I exclude from the definition of porn --- of course --- mere descriptions or depictions of nakedness or sex, which might be perfectly OK for purposes other than prurience.
This may cast some light on the subject: I've had to do a lot of thinking about where to draw the line, because I wrote a novel which included some sexual description --- necessary to show why the characters thought and (re)acted as they did.
Three friends who read the manuscript thought it went too far. One e-mailed me that, for him, it sparked fantasies which he'd been trying to tamp down; two said they thought it was emotionally overwrought (but not arousing to them.)
But a dozen friends who read it thought the sexual/romantic sequences were "just right" in that they depicted experiences by way of suggestion and somewhat veiled language, without going so far as to sprinkle erotic itch-powder on the reader's mind (or other sensitive parts.) All of these "approvers" were sexually wise, sound, conservative people who were wide and deep partakers of literature and the arts, so I trusted their judgment.
And I would now resist any suggestion that I delete or change those passages. They were not arousing to 95% of my manuscript-readers, and thus they were not porn.
"The line" between artistic depiction and porn, then, is certainly at different places for different people. I suggested to my singular, somewhat-bothered-friend that if such depictions bothered him, he should stop reading right there, and no hurt authorial feelings.