I also know two people with PhDs who smoke, they are the kind that limit themselves to smoking in the evening. But then I also know at least 4 people in their late twenties who prefer weed and gaming over getting a job. Both groups are the exception.
Most of my friends still smoke so I'm fine with it, but I'm 100% convinced that people who try to legitimize it as some sort of productivity thing, and try to sell weed usage as anything other than "I like how it makes me feel", are lying.
Though judging from the other comments here maybe I'm just wrong. Maybe it's because I like to do stuff like maths and programming in my free time which is absolutely impossible while high.