My fundamental problem with Libertarians boils down to one woman. It has been my general experience that you can discuss civil liberties with Libertarians all day. You can heartily agree and shake hands on the principle of the golden rule. But at some point you put forth some form of tragedy-of-the-commons dilemma (healthcare, public safety, infrastructure, courts, you name it) and they lick their thumbs, page through Atlas Shrugged and start pontificating about how greed is good and that people have the right to their own self-determination and basically reveal themselves not to be self-determinists but to be neo-feudalists who think they'll win because they've thought about it the longest.
Yeah, I can't find a nice thing to say about Ayn Rand. Bad philosophy in expressed in worse novels. But I think around the edges people start with dissatisfaction and latch on to the theory that seems to best express it, so "is this theory bullshit" isn't the right question to ask (they all are), the question to ask is "why have you latched on to this theory." Now, I think guys like Alan Greenspan probably latch onto it because feudalism isn't so bad if you're on top, but I don't think that's the motivation for the rank-and-file libertarian, who are for the most part not on top and know it.
It is my considered opinion that the overlap between libertarians and preppers is not coincidental. Libertarians espouse, above all else, the principle of fairness and resist, above all else, the concept of externalities. They are self-determinist to a fault and are generally resistant to bureaucracy of any kind for any purpose. The average libertarian thinks they would be far happier a hundred and fifty years ago when land was free and self-determination was the watchword but the average libertarian also resists the notion that "free land" is a consequence of a totalitarian cavalry hell-bent on genocidal conquer. The smart ones will wiggle back to "well of course we need an army to protect our civil liberties but only to protect our civil liberties" but will always change the subject when you point out that private armies are never used for good.