to kill the black market...

If the "authorities" really wanted to kill the black market in marijuana they'd encourage farmers to cultivate industrial hemp. Cross-pollination between low- and high-THC strains would make it much more difficult to grow 'sensimilla' ("without seeds") pot, so there wouldn't be criminal plantations in the back country.

Let people grow outdoors as much as they want, and the market will flood so that the indoor (high electricity bills, major carbon footprint, chemical "Frankenweed") grow scene would become much less profitable.

Prohibition of marijuana was motivated by the industrial competition it posed. Ending prohibition of industrial hemp will eliminate that economic block and solve a lot of problems all at once.

Eliminating the DEA and the IRS will do more to recover balance than locking up all the drug dealers in the world.