Just so you know, I speak as an avid user of marijuana as well.
First off, marijuana IS a drug and it IS addictive. Anyone who tells you otherwise is either misinformed or lying. There is no physical addiction but, like with many dangerous things, it can easily take a hold on your life.
THC and all the other cannabinoids inside of pot can have quite the effect on the body and you can indeed "overdose on it" as well. (Note: I'm not saying you can die from it, you'd have to smoke your body weight to do that. What I'm saying is that for the uninitiated who have too much, it can definitely cause an acute panic anxiety reaction. People describe this reaction as an extreme fear of "losing control" and although it cannot kill you (and goes away in a few hours), it can be quite the bad experience.
The main reason it continues to be illegal today is not because of racism or even because of antiquated values about pot being a bad thing. Alcohol companies make up the HUMONGOUS BULK of money thrown at legislators for the purpose of keeping it illegal. (Because yeah, how many times have you said, "Ehh, no beer for me thanks. I'm pretty baked." Or equally likely: A friend offers you a joint and you scream, "I JUST FINISHED A FUCKING SEABREEZE!" That's right, it's the same joke twice.)
Plus hey, any body/mind altering substance becoming legal today is a miracle. Lots of money has to be thrown around and papers passed and inspections made before that happens. Hell, the drug bureau probably would not legalize coffee today if it came out because caffeine in such a raw form is so addictive (physically).
Although I have seen how great marijuana can be for medicinal purposes, I am throwing that bit completely out the window. There have not been enough major, sponsored, controlled studies to throw any full-Science-weight to backing up that information. (But yeah, I have used it to cure my nausea and as a pain killer before as well. It worked great... But I'm not a doctor.)
Straight up smoking bud is also in no way a form of medicine. Most doctors would not recommend the raw, combusted smoke of an unregulated and non-scaled or tested substance. It is still SMOKING which is, in itself, a bad thing. The heat of burning pot is also higher than tobacco so if you smoke joints or a pipe, you're just as likely to get cancer as straight rolling tobacco smoked in a similar way. (Yeah, there are a ton of cancer causing agents in ANYTHING you smoke!) So use a bong or a vaporizer I guess...
Also: An assassin using weed to calm down before a kill is straight up badonky. THC will not help you perform physical tasks and it DOESN'T calm you down. Indeed, thinking and reflexes are slowed, visual tracking of moving objects is far worse, increases the heart rate by 50%, causes the formation of phlegm (a minor problem, I know, but that impedes breathing in the long run), and worse, makes you easily distracted. I can see this assassin now: "Okay. Time to kill the mayor... Oh shit, I have peanut butter on my hand. Ohhm nom... Oooooh God I wish I had cookies."
Leave the arguing to NORML
and let them do the talking.