The absence of monopoly means that you can exercise exit, even if you cannot exercise voice. The presence of monopoly means that, at most, you can exercise voice.
Neither my local supermarket nor any of its suppliers has a way for me to exercise voice. They don't hold elections. They don't have town-hall meetings where they explain their plans for what will be in the store. By democratic standards, I am powerless in the supermarket.
The exercise of voice, including the right to vote, is not the ultimate expression of freedom. Rather, it is the last refuge of those who suffer under a monopoly. If we take it as given that the political jurisdiction where I reside is a monopoly, then perhaps I will have more influence over that monopoly if I have a right to vote and a right to organize opposition than if I do not. However, as my forthcoming Unchecked and Unbalanced argues, the reality is that the amount of influence I have is shrinking while the scope of the monopolist is growing.
Federalism is the attempt to have the best of both worlds, and the original Constitutional design of the bicameral legislature was the attempt to implement it. Ronald Reagan endorsed the idea of people "voting with their feet".
The continued push toward a one-world government is the greatest threat to individual liberty.
Hat tip: Let a Thousand Nations Bloom