Induction from a single case/women should be seen (for a nominal fee), but not heard

"Common sense tells us that..." 
Actually, hard facts tell us that between 3/4 and 9/10 of prostitutes are beaten and raped, a prostitute is around 40 times more likely to be killed, and that almost half of people trafficked into prostitution are minors; common sense tells us that fantasies backed up by a single case are misleading, and that portraying such as informed analysis on one of the world's most pervasive media outlets is terribly irresponsible: journalistically, morally, politically and socially.
The introspection of someone who - by their own admission - is entirely ignorant of the subject is worthless (unless, perhaps, the subject is mathematics, logic, or something else purely analytic, but I suspect the reality of prostitution is not an a priori synthetic truth). If we want some understanding of this subject matter, I suspect facts may be more helpful. Research, reports, and facts, gathered from a range of expert bodies invariably show that Dr Magnanti is an exception, and Mr James is mistaken.

Only ignorance will allow one to speculate that the vast majority of prostitutes do not lead lives of pain, misery, exploitation, rape, assault and exploitation, because all research says they do. There are exceptions, but accounts such as Dr Magnanti's do not begin to nullify the horrifying experiences of so many who live a life of brutal, violating slavery. Mr James spins from this account a misleading global narrative that perpetuates myths which many wish to believe, but which defy the facts; by doing so, he, and by his actions Dr Maganati, contribute to this abuse.

Beyond suffering and victimhood, beyond each individual's experience, is the broader societal context in which these events take place: we live in an unequal society, where women are paid around a fifth less than their male counterparts, occupy a lot less of the top jobs, and account for more than half the politicians in only one country in the entire world. Such cold statements reflect a more pervasive, every-day problem: women are not being treated seriously as people. 

Women-as-objects are still more common in our media, advertising, entertainment and, therefore, consciousnesses, than women as thinkers. In fact we are far more accepting of women as objects. Any woman ascending to power herself will quickly be savaged or ridiculed (look at all those female Labour MPs of the last ten years, who upon touching cabinet were torn to shreds by the media), but the wives of politicians may be lauded - but only for their choice of outfit, or for having a nice smile, i.e. in their capacity as eye-candy. Watch any news coverage and you'll see Michelle Obama as the beautiful, well dressed saint, while Harriet Harman is portrayed as a crazy witch with extreme, yet trivial views. For an example, see The Independent's reaction to reviewed rape laws which aimed to prevent women being convicted of murder when they kill their husbands following years of physical and psychological abuse, while making it a crime for a man to kill his wife because of infidelity; Harman the grinch; Harman interrupting the men in that silly way girls do; Harman indoctrinating children; "Harriet Harman is either thick or criminally disingenuous";  Harriet Harman's use of facts completely disguises the truth (with a wonderful link to "Prostitutes are, in effect, blackleg labour, strike breakers. They undercut middle-class women. If men can go and pay for sex with someone like Brooke Magnanti, why on earth would they bother to put up with the endless screaming demands, the controlling behaviour, the constant low-level mental abuse, the endless tears and hissy fits of the average middle-class princess?")
Such drivel is easily satirised and the dubious journalistic standards held to account.

Behind this lies the ever popular Madonna/whore complex (and yes, I have exhibited elements of this myself), which is so deeply ingrained into our collective moralities one wonders if it may ever be removed. Women ought be saints like Mrs Obama, or Lady Diana, and be chaste, quiet and pretty, or they ought be whores and thus give up their rights to human decency. Either way they are not people, we do not treat them as ends in themselves, but as furnishings. This is what must end. This is why a handful of 'happy hookers' will make up for the exploitation of so many: the oppression is not merely an issue for prostitutes, but for us all.

When I worked on a till in Sainsbury's, I made the most of it - I was happy as I could make myself. This does not mean I would choose to be till staff. Choosing to be happy in one's situation does not make one's situation desirable in itself. If you find someone interned in Guantanamo Bay, who's determination makes them happy, does that mean they wouldn't rather be free?

But if freedom is the issue, shouldn't Dr Magnanti be free to do as she pleases, opine as she pleases, and share this with the world? Yes, yes of course she is free to do so, and ought be. But freedom entails responsibility. I am free to step into the nearest pub and kill everyone in it, but I oughtn't.

Though I ought avoid using morality as a stick with which to beat Dr Magnanti. She released her story early as someone else was about to anyway, and it's better to have some control over the presentation. Similarly, I ought be careful about judging her for entering prostitution. PhDs are incredibly expensive (why??). Funding a PhD is a huge challenge to any wannabe academic. Those with inherited wealth needn't worry, while the tiniest minority may get funding because of their exceptional record (this number is infintessimally small), most must beg wealthy corporations to allow them to research, essentially as a slave (working to not get paid, working without employment rights), whatever may be of use to that corporation. All for three letters than give some academic credibility. Dr Magnanti's part-time job at least gave her academic freedom.
And Dr Magnanti ought not be expected to lie. If she enjoyed her work, then good for her. The issue I take is ultimately not with her, but with those who wish to use her story - which endless research reveals to be an exception - as the sole evidence upon which to base a pre-conceived narrative to mislead the public, obscure the truth and justify sex slavery, rape and assault as a 'profession'.

The morality of someone selling their own body, entirely of their own volition, is a divisive issue complicated by the subtlety of societal repercussions; what is indubitable is that the cases in which this question is relevant, where the paid participant can be said to have meaningful agency in the act of prostitution, are the minority.