The first people I met that were open about smoking pot (that weren't dumbass hippy-types) were two engineers from Purdue, one of whom happens to oversee bridge construction (I can hear it now, "Tell me which bridges he's designed so I can stay away from them!").
I think the misconception is that it was the weed that made people hippies, not just that hippies happen to smoke weed. Its prohibition seems to have been based, at least from Nixon's perspective in the overall War on Drugs, on a justified dislike of the American commie culture, and arresting people for smoking pot was the easiest, and most common, way to go after them. So, it's really a result of the Culture War, more than strict prohibition.
I think the main push for criminalization of weed is coming from the alcohol industry. If Marijuana was legalized, the sales of alcohol products would nosedive .