Sure, if only narcotics were all we were controlling. But there are plenty of other schedule 1 drugs (marijuana being the most popular) that don't have this issue, yet remain illegal. Meanwhile alcohol use most certainly has a devastating impact on others, both in terms of drunk drivers, and alcoholics committing crimes to buy more alcohol. The difference being alcohol is considered "acceptable" by the powers that be, while marijuana is not.

It all boils down to them enforcing their morality on the rest of us.