Very good point. I suspect this is because libertarianism by definition is completely meaningless unless it is implemented in its entirety. Anything short of a 100% libertarian system is dysfunctional by definition.
I use the example of the "selective libertarian" to make this point. He's the guy who insists -- based on his libertarian principles -- that the government has no business outlawing drugs, but then turns around and calls on the government to expand drug treatment programs for people who "need them."
I agree that that description fits a "liberal," but not a libertarian. Or shouldn't.
I will say that there is some common ground between "liberals" and libertarians - both allege respect and support for individual freedom and personal liberty. "Liberals" undercut themselves on those principles by also supporting leftwing ideals and big government powers, which are inherently totalitarian. Libertarians undercut themselves by overemphasizing all sorts of superficial screwball causes, like drug legalization, while underemphasizing the important core aspects of their ideals, individual freedom and limited government.
Nevertheless, the libertarian ideal, that goverment's primary purpose is to protect liberty, comes closest to the ideals of our founding fathers of all modern political philosphies, and is thus in reality, the most "conservative" of them.
That fictional person wouldn't be a Libertarian.
L