Is someone deep in porn going to be swayed by a logical scriptural argument? Or will they simply try and find the loopholes in that argument and keep going - as they are operating in the realm of emotion rather than trying to find and follow God's ideal plan in all aspects of life? Might this be best countered by addressing their emotional attraction to it, at which point they will be in a position to consider the scriptural arguments more clearly?
Remembering this is quoting a fictional demon, so it's written backwards, this is good food for thought on why porn use is harmful and against God's plan, even without needing to do a careful scriptural study:
“Never forget that when we are dealing with any pleasure in its healthy and normal and satisfying form, we are, in a sense, on the Enemy’s (God’s) ground…He [God] made the pleasure: all our research so far has not enabled us to produce one. All we can do is to encourage the humans to take the pleasures which our Enemy [God] has produced, at times, or in ways, or in degrees, which He [God] has forbidden. ”
― C.S. Lewis,
Screwtape Letters
Porn is a way Satan uses a pleasure God has made in order to mess up somebody's life. That's a pretty simple reason to see it is wrong and reject it.