Besides, what's in a word? A courtesan is, in Romance Novel Land, a prostitute heroine. In the hierarchy of virtue, "whore" is at the lowest, generally portrayed as an amoral villainous woman who is beyond redemption. "Mistress" is somewhat better, provided the mistress is a fake one. Otherwise, she's a greedy amoral whore who is often found competing for the hero's affections. The difference between a whore and a mistress, in romance novels, is that a mistress is/was married to a nobleman, and that was for money rather than true love. The whore is unmarried. "Courtesan" on the other hand means that this woman is forced to sell herself, often as a means to survive, and she has finally reached a stage in life where she is at liberty to pick her clients, all of whom are harmless milquetoasts who seem to be like her Gay Best Friend sorts than lovers. Some authors go further: the courtesan, being so rich and successful, sees no reason to sell herself anymore and keeps an older male best friend as fake lover just for appearances. The difference between a courtesan and a whore/mistress is that a courtesan is starring in her own romance story and she is generally asexual when the story begins... at least until she meets the hero.
Therefore, you can call her a whore, prostitute, courtesan, whatever - the romance heroine is still constrained by the unwritten law that she is in a less happy place, sexually, than the hero when she meets him.
You know who the real whores in romance novels are? The so-called innocent and virtuous heroines who, in a typical romance novel, puts out to the hero within fifteen chapters of their initial meeting (which means a week or two in romance novel real time). We should stop calling Lusty Lizzie down at the docks "slut", because real slut is Miranda Merriweather, the supposedly selfless bluestocking heroine, who decides to get herself penetrated by a lusty Earl she barely knows because she's determined that she needs to have him just once in her life for the memories. Putting out so soon to a man, my goodness, and without the sanctity of marriage? Who's the real slut here, people? Who's more amoral, the prostitute working to keep a roof over her head or the bluestocking who decides to ask some rake to teach her tips on seducing some boring guy we all know she'll never marry in the end?
In romance novels, when it comes to the heroine, external appearances matter the most. The romance heroine can be the biggest whore in town, but if you set her up as a plain bluestocking who can't get a beau after three seasons, the reader will be tempted to view the heroine's antics as evidence of her true love for the hero. But if you have the heroine start out as a whore and even if you actually make her celibate in the entire story until she meets the hero, readers will still call the heroine a promiscuous amoral whore, write long rants complaining about the decay of morals in the genre, and post angry reviews on Amazon.
And if you think about it, who is more pathetic here? The heroine who lets the hero deflower her without any promises of marriage, despite the stigma about ruined women in the 19th century, in the name of true love - or the mercenary woman who takes time to negotiate payments for services rendered? Given that sex in the 19th century often comes with a heavier possible cost to the unmarried heroine, why do we consider a heroine freely offering her sex to the hero a good thing? I've seen readers who condemn a heroine that take birth control measures because the fact that she takes precaution is a sign that she treats sex as something less "special". But since when is being smart a condemnable offense?
Then we have heroines who, after being knocked up by the hero, decide to run away to raise the kid alone. How she is going to do this is never elaborated on because we all know the hero will catch up with her and marry her in the end. Her running away is supposed to be a sign that she loves the hero freely and she will never force him to marry her if he doesn't love her. Now, I don't know about you, but if my daughter gets knocked up and she then lets the man walk away without even asking for child support because she doesn't want to "trap" him, you'd find me in that corner in my bedroom, weeping my eyes out and wondering aloud where I went wrong because I've raised my kid stupid.
I personally do not understand the logic of historical romance novel heroine behavior, I tell you. Maybe it's because I didn't attend the Mary Balogh College of Braindead Heroine Behavior. For me, give me an "amoral" heroine who makes the hero pay, pay, pay to get to her hoochie anytime. Why do heroes have the ones who get reformed all the time? Let the heroine have a chance to play the one needing to learn how to love too! Besides, with romance hero tropes being the way they are, I find a heroine who plays such games - thinking with her head as well as her heart about the pros and cons of letting the hero into her bed - far more interesting because she's then playing the same game as the romance hero. Two people playing in a level field is always more interesting than a one-sided sexual power play.
Therefore, "courtesan", "mistress", whatever. All this is just smokescreen for the real topic at hand, topics that very few people dare to address out loud in fear of offending people: that many romance readers suffer from hang-ups about female sexuality that they project into their books, hang-ups that many of us hate to admit because the romance genre is supposed to be more about female empowerment and what not. Yes, we are talking about those readers who genuinely believe that birth control is evidence of a woman's amorality, that a woman willingly entering a sexual situation without being forced by external circumstances is a woman who is without redeeming qualities, and such. There are probably many of these readers out there, given the kind of sexual politics present in romance novels that sell the most. At the end of the day, the heroine who is aware of her sexuality and uses it as a bargaining tool, either for power, pleasure, or money, is the whore while the heroine who puts out to the hero ten pages after meeting him is fine as long as she doesn't initiate the sexual situation, become aware of the consequences of pregnancy or take precautions to avoid that, or hold the hero to his responsibility when he decides that he's too emo to pay the piper after porking the heroine.
That is why I enjoy reading erotic romances, by the way. Sure, there are erotic romances who play the same rules as non-erotic romances when it comes to the heroine's sexuality, but some authors write assertive and confident heroines who aren't afraid to play even if it means people will call them whores. These erotic romances provide me with some much-needed respite from the overwhelmingly antiquated sexual politics present especially in mainstream historical romances set in England in the 19th century.