The easy answer is that it's terrible. The female sex workers are being used in the most intrusive way: having to not only bare their nakedness, but to engage in sex acts with complete strangers whose only real qualification is how much money they are willing to spend. This violates our most basic understanding of what sexuality means, and the context in which an individual should share this most private of activities.
Sex work is certainly unsavory. It seems quite onerous in many ways. From a purely physical standpoint, there is an element of risk of personal harm, whether from violence or disease. In the sense that the act itself is utterly invasive, there is an emotional and psychological burden that must be endured. Of course, this may be less of a problem for some than others, but nonetheless it is part of the job. One surely never wants to be seen simply as a piece of meat to be bought and consumed. There seems something degrading about allowing one's normative social status to be violated for pay. To the extent that one's dignity and identity is based in having an interior sexuality and intimacy, prostitution presents a threat to the sense that, "well, at least I'll never do that".
A particular scene in the movie raised what I thought was a very important question. A group of protesters has just gathered outside the ranch's gates and Mirren's character, real life Mustang Madame Grace Bontempo, has this to say to them:
"Do you think they'd dreamed of being hookers when they were girls? No, but they've taken what life has thrown at them and they've made the best of it, OK"
A very candid statement. I imagine this is the exact sort of moral hypothetical that we all might ask ourselves when determining the morality of prostitution, pornography, or any type of sex-work, really. Would we ever want our daughters to grow up and fall into this line of work. The answer, I'm sure, is a definite "no". Therefore it would seem hypocritical to make any apologies for the work at all.
But then again, there are many jobs that I assume we would not want our daughters to perform. And yet millions of women perform them, sometimes for their whole lives. And while most of us would never consider purchasing the services of a prostitute, we purchase the services of these other occupations on a daily basis. Most of the time we think nothing of it.
For instance, working in a meat-processing plant is dangerous, degrading (you come home smelling like animal flesh and blood), and it pays relatively poorly. Washing dishes is a menial, mind-numbing job. The highlight of the day is sometimes the 15 minutes of daylight you see while carting grill grease out behind the building so that it may be sold to a pet food company. Picking lettuce is certainly no picnic (as this story illustrates quite well). Surely we wouldn't want our daughters to grow up and be stuck doing these jobs. While we may never in our wildest dream think of taking advantage of a poor girl for sex, we all order cheeseburgers, with lettuce, with the implicit assumption that someone will be washing our dish. Check please.
Something else that seems to add an even deeper irony is the fact that sex-work so often pays much better than other physically difficult or traditionally degrading work. I'm sure there are many strip clubs that pay very poorly, or low-rent porno operations. But by and large I think the hourly wage is beyond compare. Yet at some level it isn't really about the money. Because while we would all like to see these working girls be paid handsomely for their labors, our moral conception seems to have little to do with income. For instance, whether a girl is paid $100 for 15 minutes of intercourse, or $3000, seems to make little difference: the act is still generally unthinkable. Yet this certainly makes a great deal of difference to the worker.
Another great irony is that to the extent that there are girls out there who are doing sex-work, our humiliation of the work itself acts as a negative to the job. Certainly there is an implied form of deterrence here, in that society's humiliation is at least in part an attempt to shame girls from entering the profession in the first place. But once they are there, this can heighten any discomfort they may otherwise be feeling. A common complaint among sex-workers is the ostracism they face from loved ones over their occupational choice.
All of this goes back to the meaning of the work. The meaning of sex. While in the end sex-work, or at least prostitution, may truly be something that is fundamentally unhealthy in society, the "oldest profession" has always and will always be with us. As such it is important for us to at least try and understand it, with a critical examination as well of the structure of every type of labor in society, with an eye towards dignity and fairness for all.