The National Institutes of Health (http://www.nida.nih.gov/
infofacts/marijuana.html) which is the federal government's public health organizations, have concluded that as of today, we know that the carcinogens in most readily available marijuana are quite harmful to developing brains and bodies, yet do not have the same detrimental effects in adults when not used habitually. Further, the addictive properties have been found to be fundamentally behavioral in nature. In adult users of marijuana, about 9% become addicted. All the interventions available are behavioral in nature, and enjoy a very high success rate of curing those addicted.
A number of studies conducted by the NIH, funded/published by Addiction (a medical/social science journal), the National Academy Press, the American Journal of Public Health, and Aids Treatment News have all provided scientific evidence supporting legalization, at least in medicine. The evidence strongly suggests that tobacco, or alcohol, pose far more serious physical health risks than marijuana, especially given the direct links to cancer and death that marijuana specifically prevents.
Take it to the streets: if Marijuana were completely legal especially at the federal level, with age restrictions similar to alcohol and tobacco use, street-level dealers would immediately become recognized businesspeople. The dangers associated with marijuana dealing as a deviant form of employment would practically disappear.
So there's some stuff and junk for you. Enjoy your life, and if you smoke...I ain't trippin.