To address the degradation issue...I think it has to be entirely up to the models to decide whether or not they are being degraded. Nobody else can make that judgment.
I read the blog of a women who has worked in just about every side of sex-work imaginable. She has been a stripper, escort, waitress or something at a nudist colony, erotic photographer (I haven't seen much of her work, so I don't know whether it was porn, erotica, or nude art), etc. She is currently a dominatrix, and occasionally models for erotica.
She said once that the most degrading job she has ever held was as a waitress in a mainstream, family-oriented restaurant. She does sex-work because she enjoys it and felt used and exploited by the "Smile and project fake happiness" policy of the restaurant where she worked.
Recently, I read through the "Our values" section of a popular kinky porn website that has a reputation of being a great site to model for. Their policies are responsible both in terms of caring for their employees and models, but also in terms of not presenting images that novice kinksters would be likely to try out, if such things could be dangerous if done wrong. It is very clear that they care for the physical and psychological needs of their models and are careful to build a comfortable and healthy work environment.
These are the same models who are bound and whipped on camera.
In short, the models seek out this site because they enjoy what is presented. The employees of the site take great care of them. Many express a desire to return. In between arrival and "Ohmygosh that was great I want to come back," though, what is done to them is called degrading, by many people. Why is that?