While the US is passing more and more stupid laws banning consensual sex between adults, many countries in Europe and South America have legalized prostitution and bettered the lives of sex workers. I'm sure that won't happen in the puritanical, impractical US but it's something to think about for when the idiots in charge here get replaced by slightly less idiotic idiots who actually want to help people rather than pretend like they're on the moral high ground while doing the same things they outlaw for others.
If you don't know whether the person you're paying needs the money to survive, it's immoral to buy "sex." You don't know to what degree it's "sex" or they are forced into it, which is called "rape." Banning the purchase (the "Nordic model") is the same as banning other immoral acts.
It's the same with porn by the way. You don't know if the women you're watching are on drugs, being threatened by men, or just needs the money to survive. So what what are you watching? "Sex" or rape?