I've always hated prostitutes, I often go out of my way to do them harm in any game in which they appear. Thing is, I don't quite understand why. Something seems inherently wrong with licentious nightwalkers making a mockery of love, but really, so do "wholesome" relationships, as far as I've seen.
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I'm pretty sure that romance is dead, that most couples don't realize that people change as they age and they may not still love who their partner's become a decade or so later, the grand joke that is love between a man and a woman. (for lack of better words, no discrimination intended) It seems a harlot is at least honest, and, in a way, purer in his/her intentions that the average fornication junkie.
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So, responding to a natural human urge by soliciting the help of a prostitute and paying them for their service? Probably better for the soul (if we have them) than an actual relationship. Besides, I've heard a few tales about people using whores as cheap psychiatrists, some with positive results.
EDIT: Forgot this bit, choosing to sell your body seems fine, that sex slave shit is most certainly a problem. (along with any other forced servitude)