Well. One reasonable reply. I guess I should be reasonable as well then.
No that's wrong, libertarians are "like" the current government, just smaller.
But that's the crux of the problem: I haven't seen a workable definition of government that isn't like the current one, just smaller. It either devolves into anarchy, or creates a system that is indistinguishable from the current one, except with fewer laws. And that government has no system to prevent the creation of laws that would be identical to the current one.
Yes, that's the libertarian platform. The difference is in how large the government is and what its responsibilities are, not fundamental changes like eliminating lawmakers... honestly that's a ridiculous notion.
Then do explain: how does a libertarian government not become the current one? I mean, outside of being fully staffed by libertarians, who all adhere to the same notions of government, property, and morality? Which, by the way, is the definition of sectarianism, which is hugely destabilizing to a society. Unless, of course, you further assume that everyone is a libertarian, but then we're right back to my main beef with libertarians: completely unrealistic expectations of how people work.
Somalia and Sudan both have central governments with overreaching power in the areas they control based on Islamic law that any libertarian would find abhorrent. Furthermore, there are a number of competing governments disputing territory within each country, also seeking to impose Islamic law (but, you know, the "true" Islamic law).
I can create a central government in my house that has overreaching power in areas that... well, pick whatever you want. My government doesn't matter though, because the US government has far more power to impose its notions on mine, if it ever finds out that they clash and decides to do something about it. My powers are completely at the mercy of the US government's powers. In other words, it's no power at all. Now, what if I could repel the US government's force? Well, that's completely implausible, but it would mean I could create my own government. And I'd have to, because well, that's what a collection of rules and people enforcing those rules are.
The reason that Somalia and Sudan are important is because they show what happens when a central government is unable to enforce its laws. As you pointed out, another type of government replaces it - automatically. Maybe not in the same territory, but as you said, it always starts somewhere in the territory of the old government, because the old government doesn't care, doesn't have the resources to care, or can't enforce the fact that it cares. In the case of Somalia and Sudan, it's a combination of all three.
There are two reasons that this process matters. One, it shows how a new type of government can come about very quickly. Two, it shows empirically that the new governments always take a very different approach to ruling. More islamist, less authoritarian - whatever you want, but it's going to generally be the antithesis. And that's to be expected, since being prepared to die for the new style of government requires very strong opinions about how much different things should be. There's also the possibility that someone just decided that they'd rather be the ruler, but I'm assuming that's not what libertarians are all about.
This means that there are two reasons why failed states like Sudan and Somalia - or heck, Mexico is skirting really fucking close to that - put the lie to libertarian claims of perfect government. If libertarians would be really so keen to cast off the shackles of the old government, those places are great to start from scratch. I mean, resource wise it stinks, but at least there's so much chaos that you can quickly create your own state according to your own rules, and you'll be much more likely to be able to enforce your own ideals than anywhere else. Yet no libertarian wants to go to those places to start their Galt's Gulch. Furthermore, if libertarian ideals are so obvious, so beneficial to society, there'd be a place where it would have been tried already, and would have succeeded. The fact that all of the revolutions throughout history have never, ever, led to something close to resembling a stable libertarian society tells me that it cannot work long term or on a large scale. You can argue if you want that the pioneers in the American West were the closest thing to a libertarian society, but look what they decided to do: ditch the libertarian ideals and come together in a democracy. There are lots of reasons why that ideal died out, but at the core, it just wasn't as successful at producing the ability to defend the pioneers territory from encroachment as the alternatives.
Now, there is one more argument that I often hear when I get to this stage: yes, but the pioneers only failed because they didn't understand libertarianism, and were misled by others, lied to, and overpowered by evil, power-hungry people. I can only roll my eyes at that, because that is word for word the plaintive cry of every disappointed communist out there, ever. It's why every commune fails at some point. If your best explanation for why I should try your approach is that no one has ever done it right, and you're asking me to ignore thousands of years of history and decades of psychological research that show that it won't work... yeah, good luck with that. I hear there are some sand dunes that haven't been claimed yet. Go try your luck there. Just do it without me.