I have had friends drive home drunk, and no, not all of them made it home causing no harm, and most have stopped because of that incident. BAC has NOTHING to do with your argument, seeing as pot doesn't affect your BAC. Too many people think pot and alcohol are the same thing, or that they share soo many similar properties and they don't. I'm sure MOST people drive 100s of times before getting caught.
Basically, I don't think I'd be able to do 80+ hours of driving a week on Canada's busiest roads/highways, in rusted broken vans where the breaks/handling/acceleration/fucking floor are all shot to hell, if I was downing a 26er every day as I cruised. However I used to smoke while driving constantly (new bowl per album basically). This also includes city driving in my own car since I was 17.
For the issue of assuring everyone's safety on the roads around my area. My Licenses was taken away recently for completely unrelated reasons
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EDIT: tl;dr no one cares, and no one is swaying either's opinions "I was in this class, so I know!" "well I was in this situation, so I KNOW!"