@Khethil,
Our tendency to form moral sentiments regarding sexual behavior has been rendered vestigial by technology.
Regarding the value of female virginity: What value did female virginity ever have?
There are a lot of sentimental answers to this, but nature has not idly imbued us with such sentiments, they tend to serve some purpose, to individuals or to society, and such purpose is what I now look for. To this I immediately think of two practical answers.
First it occurs to me that placing a value on virginity is part of a larger tendency to discourage female promiscuity. This, as anyone reading this I'm sure will readily comprehend, can serve the purpose of reducing the burden that unwanted pregnancies and single mothers can place on a society.
Technology serves this purpose much more efficiently through birth control.
Second is the assurance to the male that when she bears children they really are his, the doubt of which would reduce his motivation to assist in the rearing of such offspring.
For this we now have paternity tests.
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Considering the matter a priori, my above reasoning predicts that the availability of these technologies should undermine the moral value society places on female virginity greatly. Happily (for me,) recent history conforms to this prediction.
In conclusion, while we still have vestigial sentimental tendencies to view this action as immoral (personally it creeps me right the hell out) we have no practical basis from which to condemn such an action.
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If you are wondering why some guy would be willing to pay for this, I say it is because of that very same inclination we have to consider female virginity a virtue. Placing value on any thing can lead us to regard it with esteem, or to wish to posess it, or both.
[*Edit: Before someone brings it up, I left the issue of STD's out of this post for the sake of simplicity. I feel that they would fit into my reasoning without changing the conclusion, as condom use and regular testing does much to curb the spread of such diseases. For proof compare disease rates in developed countries which have such benefits with those that do not.]