Because, as Jesse Ventura puts it, the government has to play pimp and gets angry when they don't get their cut.
That is what I am talking about!. Its only illegal because the government does not have a record for taxes to collect.
Go listen to the song or lyrics of BDP call "Illegal Business"
Additionally, as far as morality goes, I find what the government is presently doing with our $$$$ is far worse than a woman making a few bucks for giving a guy a bj.