There is a difference between gambling (which is illegal in many forms and in many places, so is punishable in similar manners to drug consumption) and drug use

There is a difference between gambling (which is illegal in many forms and in many places, so is punishable in similar manners to drug consumption) and drug use. That difference is legality. The prevailing theory is that people who deviate from what society deems (as a whole through a representative legislature) acceptable behaviors are to be punished, and since incarceration is the prevailing punishment it is imposed. Not saying I agree with the position, but there is a clear difference between legal and illegal actions at a societal level. As for what you termed selling drugs, a person who sells clearly illegal, potentially toxic, and often addictive chemical agents outside of the lawfully prescribed means of doing so are in a very separate category than the consumers of those drugs. Individuals selling heroin, fentanyl, or crack are clearly acting outside the law and in many cases doing so without regard (and sometimes explicitly benefitting from) the massively harmful effects of these drugs and the addictive attributes they possess.