I was traveling and missed out on the recent discussion so thought I'd add to it a bit.

Anyone who wants to make an argument, however specious, that prostitution is not a sin can, I believe, do so very easily.  References to 'sexual immorality' in our English translations are usually not what they appear and references to prostitution or whoredom can easily be explained as meaning something other than a female selling sex to a male.  Theoretically though, if you believe in God and the Bible, why would you want to do this rather than learn what God actually does want and allow?  Assuaging our conscience really does little good.

I do want to point out that the following is not in any way intended to say that prostitution or sex outside of marriage is not a sin.  I don't know if they are or not.  Traditional church teaching says that both are sins, however it has at times labeled numerous other things as sins, most recently any drinking of alcohol or Polygyny of any kind - neither of which are according to the Bible.  The following is intended for discussion purposes only.  Each of us must make our own determination what the Bible says and what we believe.

In looking at this over the past few days one thought that occurred to me is if Satan doesn't sometimes create sins that aren't really sins.  If he wants us to think that the bar is so high that we can't even live up to the most minimal standards of Christianity and thus get demoralized and give up entirely.

So, on with it...

A lot of what we believe about Christianity, or at least, how Christians should act on a day-to-day basis is more a result of culture and tradition than of Christianity or anything Biblical.  If you take off your cultural glasses and study the Bible you'll find that God is actually far less 'puritanical' than most conservative US Christians today.

Many Christians were taught from the mid 19th century until just very recently that drinking alcohol was a sin.  In reality there is not only no prohibition against it, but semi-support for it.  Drunkenness, not drinking, is the sin according to the Bible.  The puritans who came over on the Mayflower actually consumed great quantities of beer, and it wasn't non-alcoholic.

Similarly most Christians will say that Polygyny is a sin.  In reality there is nothing in the Bible whatsoever to support any view that Polygyny is a sin or that monogamy is the only option for sex and marriage.  Our concept of monogamy actually came from pagan Greek and Roman laws mandating monogamy.  Interestingly this mandate had nothing to do with any religious belief, but was instituted to serve a three-fold purpose of making more women available for sexual liaisons as prostitutes or mistresses, to simplify issues of inheritance, and to transfer more un-inheritable property to the government.  All but 2 of Jesus' ancestors mentioned in the Bible were polygynous and none were ever condemned for it.  In 2 Sam 12:8 God talks about the fact that he (God) gave David multiple wives.  

God also tacitly endorsed concubines.  He gave rules for how men were to treat their concubines and how concubines were to treat their men.  He never condemned anyone for having a concubine or for being one.  A concubine, by the way, was effectively a mistress or prostitute dedicated to one man.  

There are also numerous examples of sex outside of marriage that are not condemned such as in Gen 20:3 when God gets on Abimelech, not for lying with a woman who was not his wife, but because she was another man's wife.  The sin God called out had to do with adultery, not anything else.  Interestingly, the woman in this story is Abraham's wife and half-sister (and I believe also his cousin since her mother and Abraham's mother appear to be sisters.)  

[Note: The definition of adultery in the Bible and throughout history has been sex involving a married woman and someone other than her husband.  Historically a married man could have sex all he wanted and it would never fall under the definition of 'adultery'.  Even in the US this was the case until the 70's when states began changing their laws so that it applied equally to men and women.  I believe that several states though still apply adultery only to married women.]

So, from a Biblical Christian perspective, there is nothing whatsoever against a man having a mistress.  The only caveat that might be applied is that she must be his alone though this is not very clear.

Now, to prostitution.  There are numerous instances in the Bible where it specifically mentions someone having sex with a prostitute yet, as far as I know, none of these acts are ever condemned such as in Gen 38 when Judah engages the services of a prostitute.   There is no condemnation for his being a client and while there is condemnation for Tamar being a prostitute, this is because she was engaged to Judah's son and thus committed adultery, not apparently for prostitution itself.

Translational Issues.  Earlier someone had mentioned Rev 21:8 saying that the sexually immoral will be cast into the lake of fire.  If you look back to the original Greek text though you'll see that the word that has been translated to 'sexually immoral' or in some cases 'whoremonger' is the Greek word 'Pornos' which according to Strong's Greek Lexicon and other sources means specifically to 'sell a male prostitute'.  There are numerous other examples of very specific meanings being translated into much wider meanings.  I have not gone through the whole Bible however, so there may be something somewhere that does specifically make prostitution, as we know it, a sin.

Recently an argument the Catholic church has used against prostitution is that sex is only for pro-creation.  The Apostle Paul said that it is best to remain single (like him), but if you burn with lust then you should get married.  Paul is pretty specific - if your desire to get your nuts off is so great that you can't control it, find a wife and have at it.  In Deu 21:14 God actually states that if a man takes a wife (at this time there was no marriage ceremony - a man took a wife by having sex with her) and is then not pleased with her (by implication, ain't getting his rocks off) he may let her go.

Of interesting note is that both Saint Thomas Aquinas and Saint Augustine stated that prostitution should be allowed 'to protect innocent virgins and prevent society from declining into a chaos of rape.'  Me thinks our making it illegal in the US has well proven their point.

Finally, lets take a quick look at sin.  We all sin.  As I believe Tokai correctly pointed out, we are not required to live a sinless life.  AND, not only are we not required to live a sinless life, the Bible says that we can't.  Nobody in history, except Jesus, ever had nor ever will.  That is the whole point of Jesus death on the cross and resurrection.  Without Jesus doing this for us we'd all be going to Hell.