Liberal libertarianism is the original libertarianism.?

I generally agree with you but the terms capitalism and liberal are tricky. Capitalism was originally a Marxian pejorative that was associated with state protection of favored business. I think that it is unfortunate that Rothbard chose to self label as anarcho-capitalist. Liberalism of course has traditionally been associated with laissez faire. Modern free market libertarians trace their roots back to both 19th century individualist anarchism and classical liberalism. Certain 19th century anarchists such as Tucker, Proudhon, Spooner and Thoreau were not explicitly anti property and markets the way modern libertarian socialists are. The arguments were generally against the historical legacy of property being based on state privilege. Libertarians of all stripes are opposed to that. I think that the split occurred much earlier than the mid 20th century. I don't think too many market anarchists familiar with Rothbard are not aware of the leftist tradition of the term libertarian. The "libertarians" who don't seem to realize this are those who have adopted the label after hearing a conservative pundit misuse the term. Perhaps we can partially blame Herbert Spencer for the unfortunate conflation of conservatism and libertarianism. As a classical liberal and all but self described anarchist, Spencer made a political alliance with conservatives late in life as a response to the growth of the welfare state in England. I agree with you that the single defining characteristic of libertarianism is the non aggression axiom but what constitutes aggression is somewhat subjective. I don't know if Mike Gravel is the best example of a libertarian left or otherwise because he is an advocate of taxation and certain state social welfare schemes. I think that taxation is unambiguously antithetical to the non aggression principle.