So, what is Libertarianism?
Before I begin to describe what it is, I must note this: it is a political belief. I shouldn't need to state the obvious, but I have to, because of all the ninnies who try to insist that it somehow is a life philosophy and make an unwarranted fallacious extension into describing it as a personal moral ethical belief. They then go on to say that it means that libertarians are personally selfish and refuse to ever cooperate with anyone. It is similar, but far sillier, than the creationist belief that accepting the reality of evolution leads to a belief in Social Darwinism.
Yet it is basically only libertarianism that gets this rather absurd fallacy applied to it. Nobody ever says "you believe in a social safety net yet you are not out robbing from the rich and giving to the poor" or "you believe in drug prohibition yet you are not out busing meth labs." This standard is never applied to conservoprogressives yet it is always applied to libertarians.
It is not a theory of morality, except insofar as theories of morality interact with theories of government. It is really only a theory of government, what the government should do and should not do. Perhaps people are confusing it with Objectivism, because while the politics of Objectivism are indeed libertarian Objectivism is not libertarian for the simple reason that libertarianism has nothing to say about Epistemology, Metaphysics, Aesthetics, and Morality outside of theory of government.