Ok, I'll bite.
Ever watch the news lately? I do, and I hear about 2-3 people killed from drunk driving a day. I can't recall a time hearing "The driver was high on marijuana during the accident."
I've driven with potheads before, letting them drive. Some of the most cautious motherfucker's on the road. NEVER will I drive with someone who has been drinking though (to a degree, not like I'll care if someone has two beers). Which brings me to another point. Doesn't alcohol also impair reaction times? Isn't that legal? I'll be gosh darned.
And I've never smoked pot a day in my life. I'm all for the legalization of it. We'd be out of debt in a year (I'm kidding). It would also free up jail/prison space because people are idiots and keep getting caught smoking pot.