My wife and I don’t watch porn, but do sometimes get turned on by sex scenes in mainstream films and TV programmes.What is the questioner's definition of "porn" ? Apparently it's something different from "displays of other people having sexual relations".
If you watch other people in sexual intimacy, whether they are on "mainstream" media or sold to you by filthy Mick down the market, then by definition, you watch porn. Porn is porn, regardless of whether those purveying it to you wear suits and sit behind desks in White City, or whether they climb out of sewers with filthy leers on their faces.
"Mainstream" just means "what's in our current cultural setting". Your current cultural setting might be jammed full of porn. It doesn't become not-porn just because there's more of it around.
The question finished off with "is this OK?", to which the magazine replied "Yes, I think that's great!". Oh, wow. With Christian magazines like this one, who needs worldly ones?
Watching other people have intercourse is watching people have intercourse. If the question had begun...
My wife and I don't watch porn, but sometimes the neighbours invite us around to watch them making love. Is there a problem with that?... then I hope most Christians would have been able to answer "Yes, that would be a problem."
And it would be no less of a problem if your neighbour "merely" filmed their escapades and then shared the video with you later.
And it would be no less of a problem if they were not your next door neighbour, but living across the other side of town and employed by the BBC to do the very same thing. The people we see on television are people, and according to Scripture, the people you come across are your neighbours (Luke 10:25-37). If you can perceive a moral problem with your neighbour knocking on your door and asking you "fancy seeing some videos of me and the wife at it?" then you ought to be able to see no less a problem with the BBC piping the same question at you through the TV listings.