I remember reading an article or watching a brief docu on something like this awhile back. Something about teenage boys that are generally porn addicts, or watch it a lot in general. Generally if they are a virgin, the majority have erection problems when with a girl physically. That isn't just because of the porn, but nervousness etc.
Anyways, it was an interesting docu, depending on what porn each teen would watch, that may change their outlook on how sex is supposed to be like. If all they are exposed to is bdsm, abuse, choking, extreme rough sex, then there's a good chance that's how they are going to think sex is supposed to be performed that way. It also depended on their home environments and how they are raised, what other things they are exposed too etc.
There are SOOOO many factors to add in that it is unlikely that porn alone is the damaging cause. Porn is yet just another part of the problem. I can probably guarantee you that if I never watched much porn during my teens especially anal! Then I highly doubt I would be nearly as much involved in anal as I am now.