Despite being told that marijuana is a gateway drug study after study shows that it is not any more so than alcohol and for most adults it is essentially homeless. So why then is it illegal?
Two reasons why it is illegal one that's not mentioned here is that DuPont's new fibers competed with hemp fibers, but also after Prohibition ended the Federal Bureau of narcotics saw its funding cut in half. In order to avoid funding cuts the head of the agency needed to find a new substance to demonize.
In the early 70s people began to realize that marijuana was not as dangerous as it had been made out to be. But then Nixon entered the picture with the need to disrupt the antiwar community and so he began the war on drugs.