Actually, Marijuana is a less harmful drug than tobacco and alcohol (healthwise)
Marijuana is not physically addictive, unlike tobacco, and does not impair ones ability to function as harshly as alcohol. The reason Marijuana is illegal is because of the governments jailing machine know was the drug war. The drug war is a true failure, millions of innocent people in prison for possession of a "harmful" drug, which has no known health effects.
The myth that the smoke from a joint is 5x more harmful can also be laid to rest. Do you know anyone who smokes 2 packs of joints a day? No? Other countries (Amsterdam) have legalized marijuana and they seem to be doing fine. The loads of bullshit that has driven into peoples heads about the "danger" of marijuana is lies and cherry picked information.
The truth is Marijuana is the least harmful drug that one can do, with moderate use. No one has ever died from Marijuana as a result of overdosing. It cant happen.
Another reason why marijuana isn't legalized are lobbyists, tobacco lobbyists and alcohol lobbyists. If Marijuana were legalized it can be made cheaper, faster, and more effectively than tobacco cigarettes and alcohol, and it takes for less dosage to use. Nicotine users might find that pot would aid them to quit smoking = less profits. Alcohol would suffer when Marijuana became the drug of choice = less profits.
The real reason it became criminalized is because of lumber company lobbyists. Hemp (a paper making product extracted from Cannabis) is much cheaper to make than paper from trees, therefore lumber companies would lose money. Marijuana legalization would also help save our forests.
The United States Constitution was written on hemp paper.
To sum things up Marijuana is not legalized because of greed.