Jack Balkin takes us into a fictional Supreme Court opinion in Spitzer v. United States (not a real case in case you were wondering), which gives constitutional protection to patronize prostitutes.
It is based, not unreasonably on Lawrence v. Texas, which defined a "sexual liberty."
Hey, if prostitution were legal and that is how you wanted to spend your money, then go ahead. I would say that you had that sexual liberty. Your spouse might not think so, but as far as the state is concerned, you can do so.
Hat Tip: The Instapundit.