"and how are the taxpayers on the hook for the "stoners" again?"
Not every illegal drug user is going to be a burden on the system but a hell of lot of "down and outers" are hard core drug users. They place a burden on social services, welfare, emergency medical services. hospital emergency rooms and the like. I don't think you are going to find a lot of clean and sober types hanging out in the homeless camps.
We are talking about weed..... weed is legal with a "card."
Last I checked, there were plenty of homeless people before the devil's lettuce became legal. Lots of alcohol and tobacco in those camps too.