I am pretty sure they don't supply the drugs, that would make it an even worse plan. A quote from a former addict is pretty on point I think. "We're talking about a government-sponsored shooting gallery," said Mike Gimbel, an addiction expert who served as drug czar in Baltimore County after beating heroin. "It's misguided. The addict is going to say: this is cool, a place I don't have to worry about the cops. Why should an addict stop if there are no consequences for their behavior?" Treatment instead of jail is definitely the way to go, taking away any fear of arrest is not. Why not use the same money for the injection facility and put it towards treatment centers?
