Anyone who seriously believes in liberty should confront the powerful argument against it in Hobbes' Leviathan. The essential argument is correct, but radically incomplete.
Essentially, Hobbes argues that prior to (i.e., without) government, there can be not property, and no definite rights. Anyone has the power to kill or steal from anyone else (since our vigilance is finite -- anyone can be killed while sleeping), so no rational person would ever accumulate wealth or plan for the future. There would be nearly zero value to anything not immediately consumed. To avoid this "nasty, brutish, and short" life, people agree to cede authority to a single sovereign, commanding absolute obedience, and forfeit their "rights" over one another. A single recognized power is then able to enforce contracts and protect members of the commonwealth from predators, thieves and murderers. Arbitration by a third party avoids the partiality inherent in a situation where each person is the judge in his own case. This allows property rights to have a practical and nearly objective meaning, rather than being vulnerable to the subjective whim of whichever party decides to enlarge his property at the expense of another.
Since the state of nature -- the war of all against all prior to government -- is so bad because of the impossibility of property, no one is justified in disobeying the sovereign unless his own life is directly threatened.
Unfortunately (as Locke points out in far too many words), the Hobbesian Sovereign is the judge in his own case. Insofar as he threatens the properties and liberties of his subjects, he reduces the extent to which Sovereignty is an improvement over the state of nature. This constitutes the argument, on Hobbesian grounds, for liberty. Liberty is the maximal fulfillment of sovereignty, while absolute tyranny is the minimal fulfillment thereof.
Unfortunately, there are many Libertarian or Liberty-sympathetic thinkers who have not thought this through, and assume unreflectively that markets and property can best occuir without any government interference. Anarcho-libertarianism ignores the fact that government is instituted and maintained logically prior to the possibility of a market.
Markets presuppose property.
Property presupposes enforcement of property rights.
Enforcement presupposes government.
America's recent misadventure in Iraq also stems from a failure to apprehend liberty's true basis in a strong civil order. "Freedom" in the sense that we want to propagate it is not a positive institution to be enforced directly, but neither is it merely the spontaneous result of a lack of a strong government. Rather, it is the artificially level environment that results from a strong government declining to intrude into its citizens' lives, and repelling other governments. Anarchy -- at least as it has been practiced -- is merely a fertile ground for the seeds of new rules to be sown.
Remember, though, as Hume said about morality: though property rights and freedom of expression are artificial, this does not mean they are arbitrary. Rather, they are best political arrangement possible, as dictated by human nature. They have to be invented, but so did the internal combustion engine. That doesn't mean a horse is a better means of transportation.
On the Left, the confusion of corporations with governments because of their like possession of power, fails to distinguish what sort of power that is. Tyler Cowen made a similar argument once. If Classical Liberals cannot think straight about government, then we cannot coherently argue the case for liberty.