The New York Times, February 28, 2009 by Jesse McKinley
http://www.nytimes.com/2009/03/01/us/01sin.html?ref=us&pagewanted=print
“It is very hard to tax illegal vices unless one is comfortable with contradiction,” Mr. MacCoun said. “How can you collect the taxes without documenting the behavior? And how can you document the behavior without making an arrest?”