I'm going to ask you to think about something...
Let's say that marijuana use suppresses the science-y part of our brain, thereby limiting technological innovation, and enhances the artistic portion instead. And of course everybody uses marijuana and society is very rooted in the artistic forms of expression.
Imagine in this ideal society of yours that polio and smallpox not only exist, they thrive because the technology to develop vaccinations doesn't exist. Just consider it...ideals are nice, but they rarely take everything into account.