Cannabis, also known as "Weed" is in the same family as the plant known as Hemp.
This means they look almost the same and have similar properties.
The banning of Hemp also banned Cannabis because they are indistinguishable.
The reason Hemp was banned is because of the pressure the Oil and Paper companies put on the government back in the time of racism, where Cannabis was labeled "The black mans drug", this then made the government in its bias ban Cannabis and also Hemp.
A few facts about Hemp and why the Oil/Paper companies hated it.
Hemp is classed as a 'Weed' Hence the name for cannabis, but this actually refers to the fact that the plant grows similar to the pace of bamboo.
Hemp is a sub-tropical plant, this means it can grow in virtually any environment.
All parts of the Hemp plant are usable, the seeds produce oil (Which is able to be used for plastics, oil for cars) and the leaves are edible by humans allowing people to eat parts of the plant and the stem of the plant is flammable allowing it to be burnt to produce electricity or the stem can be pressed into paper.
This is the reason paper and oil companies hated it, it can grow roughly 5 feet indoors with a single sun lamp within a few weeks and outside it can grow past 20-30 feet.
This means that your cars running on oil and your coal power plants wouldn't exist if Hemp wasn't banned.
Cannabis as you know it by has multiple beneficial properties,
It is a natural painkiller.
It doesn't produce toxins like alcohol.
If you smoked it, there are no impurities when made from just the plant unlike tobacco.
People using Cannabis aren't hostile.
Cannabis as a 0% fatality rate as the plant has nothing inside it that is harmful to humans. Only what people do while on it makes it somewhat dangerous and even then its unlikely they will go hurting people as Cannabis doesn't affect anyone in that manner.
If you want an answer to your question,
Smart people understand that alcohol and tobacco are actually lethal to people while Cannabis has no adverse effects.
Unbanning Cannabis and along with it hemp would actually soak up most of the CO^2 in the atmosphere.
America has already accepted it and have multiple private and hidden farms for extensive research on the topic.
EDIT:
Cannabis has no "addiction" to it, that would all be a mental dependency rather than a chemical dependency.
Tobacco and Alcohol both are naturally addictive and cause more problems.