“Because negative effects of pornography were demonstrated so definitively in Zillmann and Bryant’s study, researchers have had a difficult time getting new studies past academic boards monitoring the use of human subjects. If a study’s effects are known to be detrimental – and there is no proof the damage can be permanently reversed – ethics boards will refuse to allow a similar study to go forward…thus subsequent researchers were unable to get new projects approved.”
- Pamela Paul, in Pornified

http://www.sociology.org/content/vol003.001/boeringer.html
“In all likelihood little experimental research has ever been done using pornography as violent or as deviant as some of the postings available on this internet newsgroup. This is understandable considering the ethical problems of exposing subjects to such materials and the possible permanent effects that subjects might suffer. The extreme violence and brutality sometimes present in postings on the internet cannot be over-emphasized when discussing the potential effects upon viewers–especially young viewers. The PI of this study found it necessary to seek professional debriefing through the counseling services offered at the university after conducting this analysis. Caution and careful preparation is advised in expanding and replicating this research.”

You might also try asking Robert Jensen how he deals with the porn research he has done and if he has any specific cites regarding doing research with human subjects. His home page is here:
http://uts.cc.utexas.edu/~rjensen/index.html