I'm not a moral realist so I think that libertarian philosophy is nothing but the most venal elements of capitalism congealed in thought, but I should add that the classical formulation of libertarianism is internally incoherent. You omit that for any transaction to be legitimate it must not only be voluntary but must also consist of the exchange of things legitimately acquired in the past, i.e. voluntarily acquired. This chain of voluntary exchange is what is supposed to grant one a title to that thing. But of course, in reality, that does not exist in the least. The distribution of things over history is primarily a function of brute coercion and happenstance. Nozick knew as much, and his suggestion is as pitiful as his scruples: we need to 'reset' society according to the Rawlsian difference principle and then begin our libertarian accounting.

In any case, I can't take seriously anyone who thinks that humans aren't interested in freedom because they want to be free to do things, i.e. I want to be free to see my family not only in that I don't want someone to stop me from doing so, but I also want the means to be able to do so. The one is more or less pointless without the other. And that obviously requires more than negative liberty. Or that, in another vein, that capitalist enterprises are not vehicles of accumulated power that sustain themselves by exploiting workers, ordered along hierarchical top-down principles. One only need step into sociological reality to see as much.