I don't think this is about weed. It's about a structure that's set up with all the wrong incentives. Police departments get to seize assets related to drug offenses with no due process. Departments are being flooded with money to buy military resources, with the provision that they use them within the year. And once they have the resources there's a whole industry of ex-military businesses designed to train departments in SWAT-like techniques.
When your local police department trains on equipment meant for executing urban warfare, is it any wonder that the wars come to our cities?