As a 25+ year habitual marijuana smoker, with a damn good job and a lot to lose if I ever got busted, I will say that it is pretty damn difficult to quit if it is readily available. I am 6 months clean now, only because all of my connections slowly became more and more scarce over the last five years, until the point I was dealing with strangers.
I cannot say how many times that i decided to give it up over the years, only to run out and pick up a bag the next day. I dont know how many times i tried to convince myself that i would save it for the weekend, or special occasions, or whatever, only to blaze through it morning, noon and night till it was all gone. I would characterize myself as addicted for a long time. Not chemically dependent, but certainly emotionally dependent.
The stuff is a hell of a lot more powerful nowadays than it used to be too, and I do believe it can, and does affect ones ability to safely negotiate a car.
...just a little personal insight into the addictive/not addictive debate. Not all addictions are the same.
Having said all that...
LEGALIZE IT!