I'm not sure how Marxism would enter into their process at all. To me--libertarianism is a class expression of "individualism" ideology.
In order to adhere to it, you'd have to ignore all of the social and historical processes that went into the making of a person at any given time.
You'd have to examine things only in isolation, with no look at the context which was at work, as the author of this article states near the end.
In order to be able to do that, you'd have to have a certain amount of independence from the negative processes that come from the system, and be able to blame anyone who does have a negative relationship with the system on their own responsibility.
I think this paragraph is faulty:
Marx too believed that only man is capable of purposive activity, and this is what separates man from other animals. However, for Marx, the most purposive activity was labour, not consumption. Man engages in productive activity for two purposes: (1) the end product of his labour and (2) the ability to exercise the means he deems most important during labour. Marx saw capitalism as alienating because in a capitalist system, the individual becomes separated from both the product and the method of production.
It is true that Marx positions labor as paramount. But not for the purposes the author states, imo. Marx and Engels knew enough about evolution and science of their time to know that humans evolved the way they did because we were incapable of surviving without laboring in common. The rise of all of our characteristics that separate us from other animals come from our need to work together to survive as a species. If we hadn't, we'd have died out.
The "Libertarian Man" is the man in isolation who comes together with others in some negotiated way to sublimate "human nature" and allow cooperation. But that isn't how history happened. Therefore all the other principles of libertarianism are suspect from being founded on fantasy.
Marx saw capitalism as alienating because taken to the historical ends it has arrived at, it is a perversion of human existence. Even the capitalists themselves are often miserable creatures, but they are driven by the demands of the system too. The only thing good about it is that it was a historical improvement on feudalism, which was an improvement on slavery. The other good thing from a Marxist point of view is that it created a working class that is capable of taking the political reins from capitalism, and also unleashed productive capabilities unheard of in previous human history.
Unfortunately the mechanics of extracting expanding profits degrades the state of workers to the point where their survival is at stake. Milton Friedman stated in an offhand way that this is part of the omelet making, some eggs get broken, but it's ok because "many" benefit from capitalism. I think that's a pretty psychotic way of looking at the world, and you'd have to be some kind of sociopath to feel that some people were just going to be expendable. (Sorry, I know this is ridonculous long...I loathe Libertarians.)