Why not legalize prostitution?

I read an interesting book, the end of faith by Sam Roberts.

He argues that drugs are illegal only because it distracts people from praying and religion. The best proof of that: a legal kind of pot (i can't think of the name) is now on sale in Canada, but not in the US. It gives, so was I told, the same buzz as ordinary pot BUT contains not THC, the illegal substance in ordinary marijuana.

For prostitution, I believe it is the same case. The state wants to regulate mores to save the (inexisting) souls of its citizens.

One of Pierre Trudeau rare intelligent quotes was ''The state has no business in the nation's bedroom''. We should keep that in mind: what goes between CONSENTING adult, be there money involved or not, is no business of the state

Jam it back in, in the dark.