I am an adult with three children. Two of which are teens, and I fully support the decriminalization and taxation of marijuana. I have smoked marijuana in my life before, but I wouldn't say this is a biased opinion.
Compared to other drugs:
http://i.imgur.com/hqDEJ.png
Cannabis (Marijuana) is less habit-forming and does less physical harm than alcohol and tabacco. Cigarettes are over TWICE as addictive as marijuana.
Here's a nice picture of the effects of marijuana:
http://upload.wikimedia.org/wikipedia/commons/1/10/Bodily_effects_of_cannabis.png
Here's a nice paragraph of the effects of tobacco:
After smoking a cigarette, a smoker will have his heart rate will increase by 10 to 20 beats per minute. Blood pressure will also increase by 5 to 10 points. Nicotine and other chemicals in the smoke constrict blood vessels throughout the body. Blood and oxygen can't move as easily through narrowed blood vessels, increasing the likelihood of heart disease or stroke. The poor circulation can also make a smoker's fingers and hands cold. The nicotine in tobacco contributes to the hardening of the aorta, a large artery that moves blood from the heart throughout the entire body. This reduction in elasticity increases the risk of blood clots and also leads to an increased risk of stroke and heart attack. Tobacco has a drastic effect on lung function. Our lungs contain mucus that traps toxic particles. Small, hair-like structures called cilia are found along the walls of the lungs; the cilia move back and forth to clear out the mucus and toxic particles. Tobacco smoke paralyzes the cilia, which leads to a large increase in mucus inside a smoker's lungs. Because the lungs aren't working properly and toxins aren't being cleared efficiently, the smoker is more susceptible to respiratory diseases such as lung cancer and emphysema. The tar that collects in the lungs also alters the DNA of cells, making it difficult for them to repair themselves and leaving the smoker more vulnerable to infection and disease. Smokers often develop a persistent cough; because the cilia in the lungs aren't working properly, coughing is the only way for them to remove irritants from their lungs. The chemicals nicotine, carbon monoxide and hydrogen cyanide negatively affect the skeletal system by weakening bones. This can lead to osteoporosis. Plus, it may take much longer for a fractured or broken bone to heal. Once carbon monoxide enters the bloodstream from the lungs, it slows the flow of oxygen throughout the body. This can make a smoker feel tired. Nicotine can cause headaches, dizziness and upset stomach. Tobacco also stains teeth, causes bad breath and decreases the ability to smell and taste. The carbon monoxide and nicotine found in tobacco may cause throat, mouth and esophageal cancers. Those who use smokeless tobacco, such as chew or snuff, are much more likely to develop diseases of the mouth, including cancer of the mouth and gums.
Anyone who says that tobacco is better alternative to marijuana has obviously not tried marijuana and is ignorant in that sense.
