Michael Sandel concludes Democracy's Discontent with the claim that “A politics that brackets morality and religion too completely soon generates its own disenchantment.” If public life has no higher purpose, we lose heart in it. It becomes a tool for corruption.
Conservatives have tried to fight this disenchantment by promoting individual virtue. This would have a social effect in two ways: we would all benefit if there were no corrupt individuals, and the project of promoting virtues is shared. The problem of today's theory of government is that the state is trying to be neutral about citizen's ideas of what makes for virtuous individuals.
Liberals have tried to fight this disenchantment by fighting the economic inequalities that stand in the way of solidarity among all citizens. Making people less unequal is clearly a social project, but it is negative, in the sense that it is removing an obstacle to solidarity without providing a common goal to be solidary about.
The early American republic did have enchanted - that is, purpose-driven - public life. We had the project of creating a democratic society out of people who had been trained to be subjects rather than citizens. That was a great project. But it has largely run its course in the world. Most states, even the most brutal tyrannies, at least pretend to be democratic.
Sandel says that when we got too diverse to ignore our different moral and religious values, we switched the goal of public life to trying to create a voluntary state that was neutral about all other goals. Sandel is right that this is not a goal big enough and positive enough to enchant our public life.