Don't know about the PED stuff, but the "safe to drive on" argument is real. I went through my 24/7 pothead phase years ago, and every stoner I knew made that argument if it ever came up. I can't tell you how many times I heard "You're actually a better driver while stoned, because it makes you more focused."
Potheads say the damnedest things. I believe part of the reason weed can't be seriously and fairly looked at, in terms of legalization, is all the ridiculous and extreme views a lot of it's advocates argue. While some of the detractors might have ridiculous "Reefer Madness"-like views on it, the extreme exists the other way as well. Extreme meets extreme, and few are willing to take an honest look at it.