The fundamental difference between the state and all other economic actors is that the state is (or rather can be) democratic, with everyone having a voice. So it is directly controlled by the populace, unlike corporations, and - properly implemented - can be trusted to operate in the interests of the society as a whole.
Every consumer can choose whether to buy products or services from any corporation or other individual.
But you don't get that choice with the government. Try to stop paying for government services.
Then, of course, a regulating state breaking up monopolies is not itself a monopolist, since it does not own all the property, nor fully command it.
The regulating state is definitely a monopolist, since it has no competition.