I will quote Terence Mckenna on this (the man in my avatar)
“Psychedelics are illegal not because a loving government is concerned that you may jump out of a third story window. Psychedelics are illegal because they dissolve opinion structures and culturally laid down models of behaviour and information processing. They open you up to the possibility that everything you know is wrong.”
Now, as literal as he was being when he said this, this applies to a lot of psychoactive drugs (Cannabis, Mescaline, DMT, Psilocybin etc). They are not illegal because they are concerned about your welfare, they are illegal because they are concerned about how they may effect your opinion surrounding social issues.
We live in a capitalist society, and economic system which thrives of productivity, do you think the elitists want to have people smoking marijuana? A substance known to change peoples perspective on authority etc?
Workers are allowed caffeine breaks throughout the day, why? Because it increases productivity. Could you imagine if people where allowed to have cannabis breaks?