"Government big enough to supply everything you need is big enough to take everything you have... The course of history show that as a government grows, liberty decreases."
-- Thomas Jefferson
I think that this is a good quote to pose to those who, these days, consider themselves to fall under the conservative banner. This is the principle of limited government: not the liberation of the markets, not the safeguarding of the personal religious beliefs of Framers from activist extension of policy... but the protection of liberty from the unchecked growth of the state.
"Whoever would found a state and make proper laws for the government of it, must assume that all men are bad by nature."
-- John Adams
This, I see as the weakness in the argument for libertarian politics. As with anarchism, libertarianism rests on the assumption that all men are good by nature -- that, when presented with unrestricted freedom of action, people will do the right thing.
How often do we need to overlook the often-quoted (and often-misunderstood) words of Lord Acton?
"Liberty is not a means to a higher political end. It is itself the highest political end... liberty is the only object which benefits all alike, and provokes no sincere opposition... The danger is not that a particular class is unfit to to govern. Every class is unfit to govern... Power tends to corrupt, and absolute power corrupts absolutely."
With unrestricted freedom of action comes the ability to abuse both liberty and license; even limited freedom presents its opportunities. Possibly the most dangerous idea being espoused by both sides of the aisle these days -- and by some of those in the standing room, too -- is the idea that were we given the power, we could do better.
Here's the catch: power can only be taken by eliminating the opposition... and an eliminated opposition leaves a void in checking the power that the victor accumulates. As history has shown over and over again, upsets in power structures rarely lead to anything other than tyrrany.
And finally, to close, some words to always keep close to one's heart, from George Washington:
"Government is not reason and it is not eloquence. It is force! Like fire, it is a dangerous servant and a fearful master. Never should it be left to irresponsible action."