Cannabis reform is proposed change to the laws concerning the cannabis plant and the drugs derived from it, whose main psychoactive component is tetrahydrocannabinol. Many arguments have been made that this drug is not particularly harmful, and indeed no one has ever died from an overdose of cannabis. But the main issue is not harmfulness but whether the person has a right to do what he wants with his own body. If cannabis consumption were to impel him to commit some other crime or tort, such as negligently running over a pedestrian, then that other offense could be punished separately; there would be no need to punish cannabis consumption itself. And in fact, many people may use cannabis without committing such offenses; some of those people have become successful politicians, rising to the highest offices, which generally requires a rather clean record.
If a behavior violates a person's rights, then harmfulness may be taken into account in determining the appropriate severity of the punishment. But if no one's rights are violated, then harmfulness is a moot point from the perspective of establishing appropriate criminal laws, because victimless crime should not be criminalized even if it is extremely harmful. To conclude otherwise is to embrace paternalistic statism. Many people's only experience with the criminal justice system is when they are arrested for cannabis possession; this criminalization of victimless behavior by otherwise law-abiding people undermines respect for the law.