Why do people automatically ume that marijuana users are unintelligent?

I agree with you. There are plenty of celebrities for example that use it. Although they might not be intelligent, they sure did know how to work the system to get rich off their es (Sheryl Crow, Joe Rogan, James Franco, etc.). Marijuana doesn't make you stupid, there is no evidence out there to support that "opinion". And any argument is invalid seeing as how it's schedule 1. People are also misinformed as to the affects of it. They go off the propaganda they were taught as children.