Complete drug legalization will involve two steps. First, making consumption, production, transportation, and foreign trade in all drugs legal. Second, making all legal drugs and "controlled substances" in pharmacies available over the counter, such that one will no longer have to pay a doctor to write a prescription.
First of all, remember that we are evaluating the government policy of Drug Prohibition, not whether a particular act of person X's taking drug Y is well-advised. It may well be that indiscriminate consumption of many substances is a bad idea. That does not mean that threatening prison time for such consumption does more good than harm.
But there is more to it than eliciting a grudging concession from the "conservatives" that beating people up for smoking something does not "work." The further importance of this reform is the complete unraveling of the ideology that it is one of the government's essential functions to protect the masses from themselves.
It has never been true that the "government derives its authority from God and is entrusted by Providence to act as the guardian of the ignorant and stupid populace," as Mises puts it (HA, 733). The implications of this truth will be felt everywhere.
Perhaps, we are not so imprudent as to fail to save for our own retirement.
Maybe we can be allowed to own and carry weapons for use in self-defense.
It is possible that businesses can almost always be trusted not to refuse service to unpopular minorities.
Entrepreneurs and job applicants might be able to negotiate a deal without the hindrance of a ton of government regulations, after all.
Most versions of government interventionism come down to the two ideas (1) that people are brainless and incompetent in seeking their happiness and (2) that the government, on the contrary, is extra-smart and needs to step in and protect them from their own foolishness.
There is a vicious circle here, too: the more the government relieves the people from responsibility, the less responsibility the people will have an incentive to exhibit. This partial stupefaction is then used as a case for still further nannying. This diminishes the incentives to the people for caring for themselves even more. Etc.
Drug legalization will signal a revolution in our thinking and may be a turning point for many other issues.