Question posed on Quora, to which I answer here since the access to commenting is restricted:
"Why is it so common to include voluntary prostitution in the category of sex trafficking?"
Some people simply can't imagine that any women would choose to do this. Because what they can't imagine cannot allowed to be, they defame and slander us as mentally ill or victimize us otherwise. Through this, our consent is rendered irrelevant, valued less and our choices can be lumped together with slavery. I don't claim that sex work is all glamorous and nice- the stigmatization which leads to a double-life or discrimination can be hard, and of course not all clients are nice (although the majority is, and with experience the idiots can largely be avoided). But I alone know so many women (myself included) who do this job and really, really like it. I don't claim that all prostitutes are like this- not by far! But even regarding those for whom it's just a way to make money and not a personal preference, consent still matters and has to be respected. In the end, it all boils down to RESPECT or DISRESPECT about the autonomy of women to decide what they can or cannot do with their bodies.
Many people also conflate the issue of generally bad situations for women in certain cultures with sex work in general. People who claim all or most prostitutes are victims often refer to the situation in third-world countries to prove that most prostitutes are exploited- after all, those countries make up the majority of the world population. Here, the bad situation for sex workers is not a problem of prostitution per se, but just a symptom of the poverty, misogyny and other social problems that pierce the majority of said society. These problems also apply to other kinds of work and not seldom to marriage. One may just as well say that most people are exploited.
An example that is currently much-discussed in Switzerland is the exploitation of street prostitutes from the Roma- minority. Roma face various forms of discrimination in their home countries (mainly Hungary): Restricted access to education and jobs lead to poverty, and landlords refuse to hire to them. This leads to resentment among the Roma, which gives rise to the infamous self- fulfilling prophecy and in turn leads to more discrimination. Furthermore, Roma culture has strong patriarchal values, which doubles the discrimination towards Roma- women. The money earned is transferred to the male heads of the family. It's the brothers, husbands and other relatives who are the pimps. Some of these women don't identify as victims, because for them it's normal to be controlled by the males in their surroundings- it's not specifically prostitution-related. If anyone has an plan that can magically fix all causes for exploitation, he or she is a genius deserving of the nobel price - but certainly attacking sex work in general and devaluing the choices of sex workers is not the solution.