For an explaination of this you have to go back to FDR. He established the governments authority to regulate virtually anything you might have or any activity you might engage in. The Orwellian logic goes something like this:
The federal government has the right to regulate interstate commerce. This gives them the right to prohibit your ownership of anything that could conceiveably be bought, sold, or trade, because you might buy, sell, or trade with someone in another state. A large part of the federal government's expansion, including the WOD is based on this idea that "regulating interstate commerce" actually means "regulating potentially interstate potential commerce".
The point is: You don't have to be a Libertarian to be disgusted with the Drug War.