I'm always conflicted on how to respond to the prostitution question, since it really depends on the situation and how it's being defined. I'll start off by saying I have no moral position on this, don't really care what religion may say about this.
In many ways all casual sex is a 'transaction' so the issue (in my mind) that money transfer or barter has occurred is simply irrelevant. The true problem with prostitution is the coercion, trafficking, drugs, and the abuse by pimps. All of that is obscene and needs to be illegal.
Then you are left with sex! I live in Thailand, where there is always only 6 degrees of separation from someone you know in the 'entertainment' industry. Thai prostitution isn't (generally) dominated by coercion and pimps. It's more a case of poor women working as independent contractors so to speak, selling sex directly to customers as Bar Girls, just to make money to support their families, not generally as I fear is common in the US to support a drug habit
So I guess the real question, in a US context is: is it the sex that people have the problem with, or all the crime and abuse that surrounds the sex?