Exchanging goods for sexual services happens all the time indirectly. Either through the buying of dinner, movie tickets, etc. Making prostitution illegal is wrong. Regardless of any social problems, people need to be free to make decisions for themselves. Government has no place making moral decisions for its citizens.

That said, the reason prostitution is illegal and buying someone a dinner for sex is not is as follows. Simple economics, you buy dinner for sex and the money begins its circulation through the system which leads to tax revenues and growth stability. You give a whore money for sex and she spends it on crack, ODs and dies breaking the cycle.

Money, the root of all oppression. There was a time in this country when people could make decisions and live and die with those decisions. Now, to many over paid bureaucrats tinkering with the system to maintain the bloat.