I had dinner last night with some colleagues. The conversation turned to the question of what could make it wrong to sell something that it's not wrong to give away. Consider: we tend to think that organ donation is a fine thing, perhaps in some cases morally obligatory. But we wince at the thought of selling organs. So it seems OK to give organs away, but not to sell them. Why?
As you may have anticipated, the conversation quickly turned to prostitution. If someone decides to have sex with another, all's well (presuming it's consensual, not an act of adultery, not an act of pederasty, etc.) . But once someone has sex with another for money, it's criminal. Why? Arguably, performers in pornographic films are having sex for money. Why isn't performing in a pornographic a crime? And so the conversation proceeded, eventually covering a wide range of similar cases.
I live in a city where people think nothing of approaching strangers and commenting on a conversation they'd been eavesdropping on. Apparently, they also think nothing of expressing disapproval of the conversation they'd been listening in on: an older man approached the table and said, "Do you really think that this is an appropriate dinner conversation?" I quickly replied, "Yes. And what is your view? Have you ever had sex for money?" As he walked away, he said, "I pray for you."