Just because stupid people do stupid things on drugs doesn't mean drugs make you stupid.
I still believe above all in giving people a freedom of choice in life. Know what'll reduce these occurrences of death and mental impairment? Education, something the USA lacks big time on. Teach people about the dangers instead of just telling them not to do all drugs. Instead our society has this giant taboo and the people that do take drugs tend to take them to get really ****ed up. The key is everything in moderation. Trust me, I smoke weed everyday (but not a ridiculous amount) and have done so for the past 3 years. The side effects are that I'm more calm and balanced in thinking, one could describe it as being more in tune with the universe. Oh, and I eat more. Yeah, there's a slight impairment in motor skill, but guess what? You get the same "impairment" from being tired.
Driving in itself is dangerous, and I'm more likely to kill someone driving tired or angry than if I've got a slight buzz (driving stoned is stupid).
So how about instead of trying to idiot-proof the place, we educate the idiots so that they aren't idiots?