There probably are attractive, uninhibited people who are excited by the rewards of porn careers -- people who are untroubled by the ethics or lifestyle limitations of making a living as sex workers, or who at the least may consider it the best of their uninspiring options. But there are probably relatively few of these people, and consumers should know who they are so they can make informed choices.
Unfortunately I don't have much in the way of studies to refute this. However, what I do have is common sense, and you only need a little of that. Let's take a moment to think about this. There is a career where you not only get to have sex as part of your job, you get to do it with attractive people for a substantial amount of money. Nooooo...who would want to do that?
It's true, there are shady porn companies out there, just like there are shady mechanics, shady lawyers, shady contractors, and shady (every career that has ever existed). But the majority of porn stars are happy with their work and the majority of porn companies have high standards and treat their employees well. Kink.com, a favorite of mine, will not shoot models that are under any sort of influence and will even go as far as stopping a shoot if they so much as think a model is uncomfortable, even if he or she insists they're all right.
It just harkens back to society's general uncomfortability with sex. It's still seen as a dirty taboo act, and it's participants as dirty people who aren't good enough to do anything else. New flash: just like with other careers, a lot of them are really smart.