If I was playing a game, and I was the general of an army, and I could tell my marines to "use stimpack", which would make them move faster and be more focused, or "use herion", which would make them move slower and be less focused. A general would never order "use herion", and plenty would order "use stimpack" daily.
But the human race is not an army, and you are not a general, or a king. You're looking at the world as an engineer looks at a problem with a set of objects. This is super common on this site - we're programmers, we love re-ordering complex systems.
Not only are people far, far, far more complex than inanimate objects, but it might turn out that issuing any orders, or banning any activity has a catastrophically different and more negative effect than you can possibly calculate. Who knows how much of our culture wouldn't exist if people weren't free to drown in their sorrows, or if people spent their lives resenting you for limiting them.
I'm not an absolutist, we should ban plenty of substances, but be very careful when considering society as a system to be optimized.