Accountability
...since you asked about the difference between private corporations and a government allegedly of the people, by the people, and for the people. By the rules of the free market, corporations and people are in a permanent state of war, and caveat emptor. By the rules of the Constitution, the government is supposed to be accountable to us.
I know, that's all theory, and your mileage in the real world may vary. Most people feel that the government is no longer accountable to the people, and nobody in his right mind would think that corporations are on our side. What's left is just us little guys, trying to avoid getting trampled underfoot.