Companies compete for your time, money, and labor. Governments have no competition.
Even if you think natural monopolies are a true facet of free markets, Facebook is not a natural monopoly. MySpace is a simple counterexample to that idea.
that's an inadequate rebuttal built on an idealization of free markets (we should strive for fair markets, not free-for-all markets).
of course competition for governments lay in ideas, thoughts, policies, and actions, not markets. in various forms of democracy, politicians vie for our votes, and that forms a web of constraints against greedy self-interest. besides, there are many goverments, and many levels of governments, all jostling with each other for the title of "best".
there's no need to revere free markets and abhor goverments (we should be vigilant of both). economic and political arenas are but two facets of our complex societies.
Even if you think natural monopolies are a true facet of free markets, Facebook is not a natural monopoly. MySpace is a simple counterexample to that idea.