While cannabis remains illegal its supply is in the hands of uncontrollable dealers who may be more concerned with profit than with quality. Health matters should be for doctors, not for policemen. That could be spent in many better ways. Paracetamol and aspirin can be abused and kill thousands every year. Alcohol is also a major cause of disorderly conduct and many crimes result.
Cannabis is different.
It is neither addictive, lethal. nor carcinogenic. Indeed, some studies have shown it protects against cancer, strokes and even from biochemical warfare. In addition it has many therapeutic and medicinal uses, it does not induce violent behaviour. Cannabis is, however still a drug, and like any drug there can be people who find its use debilitating. The only harm done through cannabis is imprisonment.