But it is essentially harmless in the context of the discussion. Smoking marijuana itself has never directly led to lung cancer or disease in a proven case. Proof of physiological addiction is something that has very little standing, in that there is conflicting information across the board. I think it's more reasonable to equate addiction to marijuana to addiction to video games or food - it's rooted in a deeper psychological issue separate from the causal factor. The same people who are addicted to weed, video games, etc are prone to addiction, something that should be addressed as a psychological issue, not a substance issue.

While I agree with you that early usage of marijuana can effect the developing brain..again, this needs to be put into context. Very few (if any) people would propose that routine use of intoxicants of any kind at an early age is not harmful to the brain. Whether it be alcohol, ritalin, weed, or caffeine pills, children who are developing should not be using these substances routinely.

Whenever the issue of legalization comes around it is always associated with the word regulation. Maybe I'm in the minority, but when people I associate with refer to the harm or harmlessness of marijuana there is a reasonable understanding that anything can be harmful given the right circumstances. Talking on your cell phone can impair driving ability, but we don't say cell phones are harmful. People can be addicted to video games, but we (at least most of us) don't say video games are harmful. If we understand that regulation and education are essential in any case similar to this, I don't think it's unreasonable to say that marijuana is essentially "harmless" given the proper context.