You misunderstand. Harm defines a crime. That's a hostility. Rape Assualt, Murder, Man Slaughter. But ethics and morality start with the core motivation. Your thread ask the question "is it immoral to sleep with a prostitute." Morality is the contemplation of social rules at a much higher level than actions but of thought and emotion. Even if you didn't pay money for the service...if it was merely "consensual" sex if you're copulating merely for your own desires then it's immoral too. You're using a person for your own selfish needs desires. It doesn't matter, money or not or if you both acknowledge your mutual use of each other. Sex is a bonding behavior. We all know that. That's why it's called "intimacy". There is another person involved yet their feelings are ignored. Yes. Without a doubt that is what we can call an immorality. If your only concern was your emotional needs and not hers or his then it can rightly be called immoral.