I thought I would chime in with my opinion and an interesting study.
It appears that Monkey's will "pay" to see female monkey butts. Now I don't know if these are professional monkey models, but I guess I can understand how that would be enticing for those monkeys, seeing as how I know plenty of human males more than willing to shell out to view human female butts.
As for me, while I admit to enjoying a nicely shaped female monkey--err human butt, I worry about the exploitation of humans, especially young females, by some in the porn industry. I don't see anything wrong with pornography and enjoy some pornographic forms. I have long thought of humans as sexual creatures. Bar exploitation, abuse or any number of harmful abuses of humans, pornography should be left to the beholder to decide what is right or wrong for them. (to clarify: I don't see anything wrong with fetish porn and other fantasies such as "masachism" style porn as long as it is done safely and by consent of all parties involved.)