In films, stereotyping people is an easy way to get a laugh.
In other movies, let's just use Grandma's Boy as an example..
Alex and Dante both smoked weed pretty heavily and sure, Alex did burn his hands trying to get a hot cookie sheet with oven mitts under the influence of pot and Dante did illegally smuggle a rare African lion into the neighborhood.
However, Alex developed a whole video game by himself. He did the programming, coding, graphics and everything by himself. Sure it took him three years, but you have to have some intelligence to do video game programming, especially by yourself, in secret, with nobody but Google to help you.
I am very much for pure weed to be legalized and taxed, just as cigarettes and alcohol are.
And like my grandpa used to say, "There's a time and a place for everything." As well as, "Too much of a good thing is bad for you."
So, smoking a joint here and there isn't terrible for you, especially if you know when enough is enough.
As for people who are overall idiots "because of weed" you have to think how they were before they started smoking it. Were they idiots beforehand? If yes, and you are still blaming the weed, then silly you.
You should blame the person, not the weed.