Many major cultural and scientific influences have been on drugs. For example many Romantics took opium regularly, although I don't think that the way these substances are managed today make it suitable for nerdiness.
Most drugs do indeed have some rather unhealthy side effects. Weed, however, does not. I've searched everywhere I could think and even got one of my Professors to let me use his EBSCO host account to search for peer reviewed journals and I found nary a one that had found any evidence that suggested any negative health effects from THC. But I never would have been able to do anything even remotely similar to research on this subject had I been high. So you do have a point. THC makes thinking very difficult.
I was high in a five hour car ride and I just sat there thinking about stuff without out saying a single word for three hours. I'm not saying THC improves your thinking, but it doesn't really decrease it. You just think of different things.