Briefly: the unifying theme of libertarianism is that the basic unit of human beings is and must always be the individual; that groups are only associations of individuals; and that human society is fairest and works best when the rights of individuals are guaranteed, and the influence of group decisions on individuals is limited. There are assumptions which must be made to support this, and implications which fall out of this. E.g., respectively, that individuals are capable of acting in their rational self-interest, and that self-organizing individually-driven phenomena like capitalism are better than central authorities at encouraging happiness and allocating resources. That's why adherents of a political philosophy are in the (unexpected, when you think about it) position of more often reading works by economists than politicians, much like atheists often read biologists.
What's interesting to me as a libertarian is that my fellow travellers occasionally develop a clear and often unexamined preference for who they would rather have their rights as individuals oppressed by. In the U.S. this preference has traditionally expressed itself in terms of the legalisms surrounding State versus Federal powers. Kerry Howley's excellent piece in Reason widens the scope in pointing out libertarian blind spots: "I am disturbed by an inverse form of state worship I encounter among my fellow skeptics of government power. This is the belief that the only liberty worth caring about is liberty reclaimed from the state...As former Fundamentalist Church of Jesus Christ of Latter-Day Saints leader Warren Jeffs can tell you, it’s possible to be an anti-government zealot with no interest whatsoever in individual liberty. If authoritarian fundamentalist compounds are your bag, the words personal agency will hold no magic for you...Not every threat to liberty is backed by a government gun." To be sure, the State and Federal powers question is not one the Constitution or its interpreters have taken lightly, and rightly so. But legal documents do not establish morality, they reflect it, and they are inevitably incomplete.
That is why, if (for example) your child were enslaved, I doubt very much you would care whether it's the authority of the Federal government allowing them to be taken away in chains, or the great State of Mississippi, regardless of whether this had happened before or after the Thirteenth Amendment was passed. To give an example of a debate that actually does have some currency: I couldn't care less whether my kids were forced to face Mecca every morning in school by Barack Hussein Obama, or to pray to Jesus by the governor of Texas. Even Ron Paul falls prey to this fallacy. I respect his Constitutional literalism, but if I had come to the same interpretation as Dr. Paul, I wouldn't be so quick to throw up my hands at the Founders' oversight and concede a States' rights to oppress its residents. I would point out the problem and suggest a fix. I don't care whether it's the Feds or a city council that's treading upon my liberty, and if there's a legal document that gives them the authority to do so, then it needs to be corrected.
It's both a difficult and exciting time to be a libertarian, largely because some of the economic events of the past year have exposed some of our unquestioned assumptions. (What do you call a libertarian in favor of the bail-out? A Democrat. I disagree, but that's another post.) There were political games that had sent libertarians into the wilderness in the years previous, particularly - and let me get out my dead horse-beating stick - the Bush administration's dedication to States' rights and shrinking the power of Federal government. Except of course where spending and deficits were concerned. And medical marijuana. And education, gay marriage, stem cell research, and abortion. But on everything else, assuming there is anything else, we were assured they were pro-States' rights.
One of the newly exposed assumptions is the role of the financial sector in a stable economy. Let the banks and automakers fail, lots of libertarians (including me at the time) said - though many softer libertarians now ask their colleagues pointedly whether things didn't work out for the better, at least at the moment, as a result of the bailouts. The recognition here is that in our current system, large financial institutions have power, a capacity for a group to exert involuntary power over individuals. This is not an indictment of the free market or the financial system, but a recognition of the distorting power that such massive, centralized institutions hold. What puts this question in a category beyond that of State versus Federal oppression is that at least you can vote for governors and Presidents. This is not the case for Citibank unless you're a shareholder, and even then the representation is not one person, one vote.
I do not feel personally oppressed by the big players in the financial sector, but it's the height of naivete to think that such enormous not-publicly-accountable institutions are unable and unwilling to warp markets and poison the political process, making a whole generation of Americans worry that capitalism is broken. I'm often tempted to add disclaimers when I write critically of the role we've allowed large institutions to play in our economy, but just like no one cares whether it's California or the United States exercising eminent domain on their property, no one cares whether it's a hyperactive bureacracy or a huge private bank that grinds their economy to a halt. What's good for GM or Mississippi is not always what's good for the country or the individual. I do what I can to advance the cause of capitalism not for its own sake but because I think it's the system that materially and emotionally benefits me personally without being immoral to others, and fortunately it seems to have this effect for lots of other people. The very moment I reach a different conclusion and find a better system, I will start supporting the new system. Market fundamentalist rhetoric (i.e., market failure apologists) gets this exactly backward. We have to save capitalism from the capitalists, and for the people. Markets do not exist without lawful institutions (non-market commons) to support them, and arguing the we should allow private institutions to distort those is a legalistic, market-fundamentalist fallacy. Adam Smith and Hayek made this case bluntly and today Simon Johnson makes it in the context of developing-world financial sector patterns afflicting the U.S. Who cares who's taking away your liberty or the system that it depends on, whether it's a senator or a banker?