if you smoked a joint (or 6 joints, whatever) with no tolerance you'd probably just want to eat a twinky and have a nap instead of driving.

even if you didn't, your motor control wouldn't be nearly as impaired, nor would your mental faculty.

your judgement also wouldn't be as impaired as having a 6 pack of beer with no tolerance, making it even less likely you get behind the wheel while too intoxicated.

I'd call that a "false" equivalence, not a rough one.