I smoke and I've got a 3.4 gpa in electrical engineering at a top 10 rated engineering school. It doesn't kill brain cells or make you dumber, people just get too wrapped up in the stereotypical culture of it when they are young. I didn't start smoking until I was a freshman in college and I'm a junior now and my grades have improved since I started.
I'm not always high when I play but sometimes I am.
and for perspective, a 3.4 gpa in EE might as well be a 4.0 in something like accounting. If you have like 2.8 or above you get internships thrown at you like they don't even care.
It's just all about your surroundings. You think pot is the devil but it's just a plant. Other people worship pot like its the only thing that matters. It all depends on who's around you when you start and how you were brought up. It just so happens that I can swing it without bringing myself down, and in fact it kind of picks me up.