There are two sides to the argument, and they are both right - and both after the same fashion.
Let's consider the teenagers' age bracket - as it would be really wrong to even think about trying to say that there's good kiddy porn: that's awful, counter-nature, and illegal in most countries. No, let's hit the 13+ age category.
And before people start complaining, this is the average age for puberty, and in several countries, not all of them retarded, it is also the age of admissible first sexual relations, or at the very least, when sex ed takes place in schools; I'll use it as the minimum age where the two domains may cross on a purely 'intellectual' matter - that's a fact, you may disagree with it, so do I, but to each his own. Also, think about it: in most Christian countries, you can get married and have sex before you can enlist - or drink alcohol. End of digression.
Like there are games that are very good at developing thoughts processes, deductive reasoning, situation awareness, imagination and reaction time, there is tasteful porn out there, that, on top of purely 'artistic' (funny, dark, detective, instructive...) considerations, show proper practices (use of condoms, careful handling of the sex partner, accent put on sensuality, do not forget foreplay, both partners are equal in the practice...) - and there's crap: mindless violent games with gore and blood making you score points, and fap-till-Silicone-Bimbo-squeals-and-it-squirts porn.
It is also worth noting that in countries where sex ed doesn't exist and porn is forbidden, relationships with sexual encounters are usually quite unsatisfying, and more often than not, for the women especially: sorry guys, but it's true: fast, hard and rough are not much of a thrill for, and can even hurt, your female partner - who may actually enjoy this kind of 'move' if you take your time with foreplay, or pay attention to her mood.
It's like a super combo in a fighting game, if you don't grow your 'super' gauge or farm for skills and level up before you go to task, you will get suboptimal results, or even a miss. In both cases, you get a 'game over' - and there are no save points nor continue spots in RL.
In short, good porn can be used as an efficient sex-ed tool (medium and advanced; basic is still better out of a few diagrams), like good video games can be used as central nervous system development tool (medium and advanced, too: basics come from real toys - not that kind, pervs!).
In both cases, they can be used as reality simulators/demonstrators; they need to be correctly tuned however, so as not to induce a distortion in reality perceptions. It comes down to the same thing though, and since this kind of subject is worth more than a couple of books, I'll conclude with a very simple to understand sentence:
bad games and bad porn are bad. Good games and good porn are good. Adults decide what's good and bad. Please be careful when taking a decision for your kids who don't know better.
@aracheb: a comic book author once wrote (transl.): 'a beautiful love story comes with a beautiful sex story. And reciprocally.' From experience, he's right.