Actually they are, or at least they would like to be. From the Libertarian party platform:
As Libertarians, we seek a world of liberty; a world in which all individuals are sovereign over their own lives and no one is forced to sacrifice his or her values for the benefit of others.
Consequently, we defend each person's right to engage in any activity that is peaceful and honest, and welcome the diversity that freedom brings. The world we seek to build is one where individuals are free to follow their own dreams in their own ways, without interference from government or any authoritarian power.
The only legitimate use of force is in defense of individual rights — life, liberty, and justly acquired property — against aggression. This right inheres in the individual, who may agree to be aided by
any other individual or group. We affirm the individual right recognized by the Second Amendment to keep and bear arms, and oppose the prosecution of individuals for exercising their rights of self-defense. We oppose all laws at any level of government requiring registration of, or restricting, the
ownership, manufacture, or transfer or sale of firearms or ammunition.
Whenever any form of government becomes destructive of individual liberty, it is the right of the people to alter or to abolish it, and to agree to such new governance as to them shall seem most likely to protect their liberty.
- "No rulership or enforced authority."
- "A social state in which there is no governing person or group of people, but each individual has absolute liberty (without the implication of disorder)."
- "Absence of government; a state of lawlessness due to the absence or inefficiency of the supreme power; political disorder."
- "Absence or non-recognition of authority and order in any given sphere."
- "Acting without waiting for instructions or official permission... The root of anarchism is the single impulse to do it yourself: everything else follows from this." 
- Anarchy is the basic rule of a no rule society.
From the pamphlet Anarchy, published in 1891:
Anarchists generally make use if the word "State" to mean all the collection of institutions, political, legislative, judicial, military, financial, etc., by means of which management of their own affairs, the guidance of their personal conduct, and the care of ensuring their own safety are taken from the people and confided to certain individuals, and these, whether by usurpation or delegation, are invested with the right to make laws over and for all, and to constrain the public to respect them, making use of the collective force of the community to this end.
In this case the word "State" means "government," or, if you like, it is the abstract expression of which government is the personification. Then such expressions as "Abolition of the State," or "Society without the State," agree perfectly with the conception which anarchists wish to express of the destruction of every political institution based on authority, and of the constitution of a free and equal society, based upon harmony of interests, and the voluntary contribution of all to the satisfaction of social needs.
Read the pamphlet and them read the party platform. Do you see the similarities? I will give the Libertarians credit, at least they were smart enough to throw in some approving references to the Constitution, but the approval is at best hollow if you accept the idea that every individual is individually sovereign. If that is the case then any law which a person feels infringes on his “life, liberty, or property (or in Jefferson’s wording ‘pursuit of liberty’)” does not need to be obeyed.
I should add that I am not a political scholar , but I have read Locke (referenced in the original post, as an inspiration for Libertarians) and I don’t recall anything about limited government in his Second Treatise. What I do recall is his idea that for the government to be legitimate it must represent the interest of the citizens. If it stops doing so then it is the right of the citizens to rise in revolt. This is echoed in the Libertarian party platform. I also don’t recall Locke advocating this idea of individual sovereignty. In fact he expressly advocates the idea that citizens must give up some sovereignty to form the civil society. Pointing this out will probably be as popular as pointing out that in “The Road to Serfdom” Hayek accepted as legitimate both the idea of welfare and nationalized health care.