When the drug effects volition, legislation and discrimination of that drug is appropriate.
Expressed another way, if the drug causes harm and its use causes addiction, such that a person is no longer has liberty to decide not to take the drug, then removing restraint from its access condones the removal of liberty.
In the 19th century, most of this stuff was legal. Laudanum (as one example) was highly abused and rampant in this country. There was a reason a 100 years ago our country did this.
Keep your Nanny State hands off my coffee.