Okay. First, no one's arguing that marijuana use isn't pervasive. Rather, I think it's pretty obvious that its use IS pervasive, to the tune of over 45% of people in the USA 12 or older have used it, and in 2009, according to the Fed, we're looking at over 16.7 million "past month" users. That's a lot of people being criminalized.
Second, I think it's really odd that you would change a critical word in the quote. "Research has shown that approximately 9% of people who used marijuana
may become dependent. The risk of addiction goes up to about 1 in 6 among those who start using as adolescents, and 25-50% of daily users." Huh. I guess that wasn't definitive enough for you. A little dishonest, though.
http://www.drugabuse.gov/tib/marijuana.html Once again, the language is inconclusive. Is it good for you? Clearly not. Is it anything at all resembling meth? No. Not even close.
Finally, looking at the addiction rates, alcohol has an addiction rate of about 5% of the total population of drinking age Americans. That's about 1 in every 20 people... not just people who drink. All people in the USA. The rate of people who abuse alcohol is much higher, classified as alcohol abuse, but not addiction.
And again, no one's saying that it's a vitamin. The point isn't that we should legalize it because it's a wonder drug. The argument is that usage is already pervasive and that the prohibition itself is causing more problems than the substance, much as the prohibition of alcohol caused more problems than it solved.
At what point does something become a medical exception? Serious question. For example, I train in BJJ, and a carotid choke is considered an extremely safe submission. Most people do just fine, but there are a few for whom it's potentially fatal. The number is statistically so small that it's considered more of an act of god than a legitimate risk. I don't think I'm being clear. I don't mean to dismiss the deaths or the risk. The point is, at what point is something so unlikely that it's not a real risk. Like being struck by lightning. Potentially lethal, but not something that is at all likely.