Pope Francis said prostitues are always slaves and paying for sex is immoral and it's like torture. http://abcnews.go.com/International/wireStory/pope-francis-condemns-prostitution-torture-53848648
Every moral argument you can make against prostitution could be made against pornography as well.
1) Prostitutes are often exploited/trafficked. You can never be sure if one hooker is exercising under her free will or is being forced by a criminal racket. But it's the same with porn actresses! If porn actresses aren't allegedly as subjected to exploitation as hookers maybe it's because pornography is regulated unlike prostitution!
2) Prostitutes are never free to do their job. No woman would spontaneously do such a degrading thing as selling herself for sex. Besides the fact that there's a long list of works as undesirable or even more undesirable than prostitution, the same can be said of pornography. Porn actresses must do several films where they have multiple intercourses with multiple actors. Where's the practical difference with prostitution?
It's almost like pornography is an already established industry and those who profit from it have every interest to keep it regulated while those who profit from prostitution have every interest to keep it illegal. So they feed the propaganda machine including the Pope.
All the considerations I made above are valid for male prostitutes/pornstars as well.