Oh, I wouldn't be as 'blunt'
as Meanstreak, but I can speak with authority that driving with marijuana in your system is a completely different equation than driving with alcohol in your system. Here's why.
ALCOHOL IS NOT MARIJUANA. MARIJUANA IS NOT ALCOHOL.
They are too completely different substances.
The primary thing they have in common is that people use them both for relaxation and 'partying', for lack of a better term.
Other than that, there's little resemblance.
But due to that one common use, much of the public slots pot and alcohol in the same vein, thinking, "Driving with pot in your system is pretty much the same as driving with alcohol in your system". It's a very inappropriate analogy, but that doesn't stop politicians and drug prohibition supporters from flogging it for all they're worth.
There's been lots and lots of research on this topic and not one peer reviewed study demonstrates significant impairment for drivers who have recently used marijuana. In fact, most conclusions indicate that pot-influenced drivers simply slow down a bit and otherwise make any neccesary adjustments to continue driving safely.