I don't think porn CAUSES rape, but I guess it can trigger it or 'inspire' it for want of a better word. What I mean is, I think it has an influence.
For example I have struggled with eating disorders in the past and find the media, EG superskinny models, diet shows etc really unhelpful and even triggering. I don't think they have CAUSED my eating disorder but they definitely haven't helped.
I feel the same might be true of porn, and I'm not a massive fan of it personally, in essence there's nothing wrong with it but some pretty sick things can stem from porn, eg rape which is apparently 'acting', hardcore S&M, I don't think things like that are healthy. Just my opinion.