If California voters pass Prop 19 next month, they will have set the stage for a valuable legal change that goes beyond the obvious. Ending marijuana prohibition is, itself, a wise and worthy goal, but the resulting conflict between state law and federal law will provide an opportunity to reverse the centralization of power in the federal government.
By asserting their state's sovereignty, Californians will have opened a new front in the fight for federalism. The FBI simply doesn't have the resources to enforce the federal ban on marijuana. Without the collusion of the state and local authorities, the federal government will be forced to either carry the burden themselves or follow the state's example and adopt a more sensible policy.
That sort of libertarian assertion of states' rights would be a major step in rolling back the power of DC.