Full disclaimer: I am male, married, and do not cheat on my wife.
My current marriage is my second, and I never cheated on my first wife. In between my first and second marriage I had one girlfriend, and I didn't cheat on her. I take fidelity to my partner very seriously, and expect the same of her.
Before my first marriage, however, I availed myself of the services of a prostitute, twice, legally, in a Nevada brothel. I paid a professional sex worker for sex, and enjoyed myself. Whether the prostitute enjoyed herself I cannot say. She acted as if she did, and I'm fairly certain she enjoyed my money at least. We committed no crime, so as a customer, a "john", I'm confident I left no victim behind. So what's wrong with prostitution?
As long as it's legal, I can find nothing wrong with it. It's the laws against prostitution that I have a problem with. They make no sense. They are laws that attempt to legislate morality, and that's an impossible task, since morality exists only in the mind of the beholder. I would consider it highly immoral of myself to cheat on my wife, but I could never hold a stranger to my own standard. If some other married couple agrees that either partner may partake of extra-marital sex, what possible business could that be of mine? Even if there was no such agreement, their sex lives, monogamous or otherwise, are still none of my business. Sex between consenting adults should never be illegal. I may consider prostitution to be immoral, but that gives me no basis to enact a law criminalizing it. Farting in public may seem immoral to you, but mere distasteful behavior on my part is no grounds for arrest and prosecution on yours.
Legal prostitution, properly regulated and controlled such as in Nevada, protects both the sex worker and the customer. It also protects the public. A legal sex worker must obtain regular and frequent medical certification that he or she does not have any communicable disease, and is not allowed to practice if the provisions of that certification are violated. A legal sex worker is required to take steps to prevent the communication of disease from the customer, by pre-sex testing and the use of condoms during sex. Legal prostitution takes place in a safe work environment, protecting everyone involved. Legal prostitution prohibits minors from participating, thus serving the public good. Legal prostitution is taxed, and those monies fund the public treasury. Legal prostitution makes sense.
Criminalizing prostitution makes no sense at all. How can it be legal to make pornographic videos, where everyone makes money, but if I just pay you to have sex with me in my motel room with no moviemaking involved, that's a crime?
If prostitution was legal everywhere in this country, Governor Eliot Spitzer may still be forced to resign, but at the worst it would have been from embarassment over marital infidelity. The question of criminal behavior would have never come up.