There is no "libertarian" drug policy there is a libertarian stance on what that policy should be. The drug policy the libertarians espouse can never be implemented in this country without inevitably becoming a liberal playground of drug treatment and victimization. The drug issue is just a minute example of why the libertarian "solution" to governing would end with a liberal outcome. The only way to have a libertarian society is to put into place a rigid "social Darwinism" that once in effect would cause a massive backlash.
But how is it any different from what you described as liberty with accountability in relation to drugs?