There are a number of reasons for the illegality of Marijuana, most of which are based off of questionable research in the past and Propaganda. In this answer, I will discuss the biggest arguments for the illegality of cannabis, and why they are, for the most part, false.
The first reason for the illegality of Marijuana is the supposed physical harm that the herb causes the human body:
Many opponents of Marijuana claim that the plant causes death in the brain cells; this is simply not true. The notion that cannabis kills brain cells was brought about by a poorly conducted scientific study on monkeys. Not only that, but many of the facts in these experiments were exaggerated to fit the Government's goal of eliminating the herb once and for all. As a matter of fact, in a recent study (recent in comparison with the studies that were conducted in the mid 1900s) by Dr. Robert Block and several other researchers, reported that there was no negative effects of Marijuana on the brain.
"The marijuana users showed no evidence of cerebral atrophy [brain cell death] or global or regional changes in tissue volume (Block)."
Another myth about Marijuana's effect on the body is the supposed addictiveness of the plant. Marijuana is not physically addictive. Masturbation is more addictive than Marijuana. However, that is not to say that some individuals will not develop a psychological need for the plant. Cannabis affects all individuals uniquely, however Marijuana is, in the general sense, a safer alternative to many things that are legal, such as nicotine in cigarettes.
There are some things that bear some relevancy. Marijuana does have short term effects on memory and motor function (these effects vary in duration based on the person). Driving for instance, is a task that is affected by marijuana use. The user must take responsibility for her or his actions so they do not hurt themselves or anyone else.
Only with unadulterated scientific research will we discover the true effects of marijuana on the body, but we can be certain that most of the mainstream claims about the harmfulness of marijuana are bogus.
The other reason for the illegality of Marijuana is the propaganda against the plant:
Since the early 1900s, many governments have launched campaigns against marijuana under the guise that the herb is a drug, and that is it obscenely dangerous. Propaganda in the 1900s has (in retrospect) teetered on the edge of absurdity as such propaganda has assimilated emotionally charged words (like; madness, devil, evil, insanity) into the meaning of Marijuana. See the links below to find samples of the propaganda. There is an excellent article on www.drugwarrant.com that describes in detail why marijuana is illegal from a social and political point of view (link posted below).
While there are still many many people that cling to the dogmatic view that marijuana is evil, there is a definite truth to be had about marijuana; and that truth, as it stands now, is that Marijuana is not a killer drug. There is still much scientific research to had before marijuana can be fully understood, we can be certain that it is worlds safer than the drugs that are legalized by the bureaucracy (like the aforementioned nicotine and ethanol. Even caffeine in soda is a mild psychoactive drug). As for the illegality of Marijuana, it is left up to the people whether or not to see through the propaganda and demand a cessation, or to accept the current views as the right ones.
Sources
Block, Robert I., et al. "Effects of frequent marijuana use on brain tissue volume
and composition." NeuroReport: For Rapid Communication of Neuroscience Research 11.3
(2000): 491-496. PsycINFO. EBSCO. Web. 18 Dec. 2009.
http://n2.cdn.spikedhumor.com/1/240000/37535_beware.jpg (Propaganda from the early 1900s)
http://www.erowid.org/plants/cannabis/images/archive/marijuana_propaganda_novel1.jpg (The cover to an anti-marijuana novel)
http://cndls.georgetown.edu/applications/posterTool/data/users/reefer_madness.jpg (A laughable classic movie about the effects of marijuana. This propagandist movie may be found on popular video sites)
http://www.drugwarrant.com/articles/why-is-marijuana-illegal/ (A nice article that describes the events and people behind the illegality of Marijuana)
Probably not. But smoking "pot" is. Not only is it illegal (in the US), it is potentially lethal, although there has NEVER been a recorded "pot" overdose or anything of the sort.
Yes. Pot affects your body. It harms the brain, lungs, central nervous system, and can cause cancer. It is also illegal and can result in an arrest.
bongs are sold under the legal idea that people are smoking tobacco with them. really, who smokes tobacco in a bong…
as soon as we started smoking pot as soon as we started smoking pot
smoking veryday and smoking by your self
probably, smoking pot screws up everything about you
because i was smoking pot once and got hit with a stone.
yes, smoking pot with anything is life threatening.
Eat pot.
no
Smoking is illegal.
There is no way you can die from smoking weed!