I don't believe this is true at all. The Constitution was constructed not to thwart the will of the people but to prevent the abuse of power among those who would use government power to infringe on the liberties of the people.
Our founding fathers meant to limit the power of government, not the liberty of the people, quite true. But they also meant to insure that the liberty of some would not interefere with the liberty of others, that is where they meant to restrain "the people." And that the majority would not, as you say, vote to infringe liberty
Our founding fathers certainly recognized that the "will of the people" could very easily come to include such things as voting away liberty, voting away the liberty of others, or even voting for themselves a share of the possessions of others (now commonly accepted). So I think that is what Diggins meant when stating that the founding fathers meant to restrain the will of the people.
I think it is no accident that the Left so frequently stresses "democracy," that one so frequently hears leftists and socialists demanding this or that new power for the state, because it is the will of the people. I've even read an assertion by a socialist that since the people and the government are the same, then the power of government must be absolute. The framers of the Constitution clearly foresaw that line of thought.