Cocaine does solve a societal problem: the cult of performance pushing people to their limits. Without cocaine, there would be more burnouts and depressions (right now; I am not talking about long-term).

See also the role of "soma" in the novel Brave New World.

People take cocaine voluntarily. It solves a problem for them, at one point at last (addiction is as much a psychological problem as a physiological one). It is the same as doping in sports. Maybe you think of junkies in the streets when you think of cocaine and see only the problems it causes, but there is as much if not more cocaine users who are right now successful executives and colleagues right by your side, who can still hide well their use, and have enough money to buy good grades of drug, and a stay in a rehabilitation clinic when things get out of hand.