It's important I first point out that society at large does not accept pornography very much more than sex beneath age of consent. I realize that porn is getting some acceptance now, but it's still disdained enough.
The acceptance of sex appears to be turning more and more on whether its consensual. That's definitely the plurality opinion on this board (the so called "elite" opinion you which you refer). The notion is similar to a "contract." A cornerstone of consensual sex is age of consent. Age of majority is in it somewhere, but statutory and case law is an incredible mess right now. I think it will get more orderly when there's more tolerance of sex, but being in flux about it, of course there are plenty of "mixed messages."
What you said about fantasy effecting reality. That has been argued a lot about many other things. About violent video games, about violence in movies, and yes, apparently about sex, too. Whether the messages are mixed or not, what would the alternative be? Can you think of another one besides the Orwellian theory of "thought-crime?"
The other thing is, as tempting as it might be, you shouldn't take individual choice out of the matter. For me, I've looked at pornography for over 30 years. The only thing it has added to my sexual repertoire is Russian and Greek. If the hobby is the question, I could never see why prostitution, per se, was wrong. Even as a grade-schooler. Mary Magdalen's story was really incomprehensible to me.
For individual choice, if I watch porn and the woman looks too young, I turn it off. The only "teenage" girls I have fantasies about are the ones who were teenagers when I was that age.
However, I consider that attraction to teenage women is just something in males. I don't consider it to be on the same scale of wrong as child molestation-- or teenage prostitution. It still turns on the theory of consent (and also that the guy serving time is probably better than making him marry the girl, or worse, having the parents shoot him). I'm shocked at the number of hebephiles (guys turned on by teenage girls) and pedophiles being uncovered, but the difference now is probably that we're catching the guys.
However, when you bring up teachers having sex with their students I have to say I think the difference is people are more alert to it. When I was growing up, it was going on. I know a teacher who married one of his students a year after she graduated. People probably just weren't looking for it. She just happened to be the most spectacular looking girl in the school
Last point about fantasy effecting reality, I'm not a psychologist, but IMHO, fantasy probably has a paradoxical role in human behavior. I think there are perhaps two different kinds of fantasies: deliberate and compulsive. Sometimes you have deliberate fantasies which you can have while knowing that you won't commit the acts. It's done willfully to more or less to act them out harmlessly.
The compulsive ones, though, come to you whether you want them or not and guide behavior and make you compulsively watch things incite that replay the fantasy. Suicide ideation is one type of compulsive fantasy, and in the same way, it can soon drive behavior. Those are the ones that need to be detected.
So, as with any other part of our media, for some people, yes, porn can cascade into behavior. Again, people have to be alert to the effects in themselves, use their wills, get help if necessary and watch for these types of things in other people.