I'm not sure if you're understanding what an LLC is, or it's purpose. I doubt Stephan, et al. does either, as described.
Typiclly, LLCs are the smallest businesses, followed by the S-Corp, then Corporations, and finally, publicly traded corporations.
An LLC can be sued. Easily. Most businesses, LLCs included, carry or are required to have general liability insurance. If it can happen, there is insurance for it, and the authorities want you to have it, trust me.
An LLC is simply a way to easily and legally separate your personal assets and liabilities from your business assets and liabilities. There is nothing that special about that.
Imagine you run a business with 10 employees. You make a sale, your engineers design the product, your office manager fills out the order, your copywriter makes an instruction sheet, your workers build the product, and it ships. Something goes horribly wrong, and it hurts your customer and blows up his building. Many people in the entire process could be at fault. As the owner, you may not be personally at fault at all. But we like to use the old "buck stops here" mentality, so it's all your fault. Your liability insurance will kick in hopefully, but perhaps the damages are so great they exceed the limits. So now you must sell off your business assets and fire your employees to pay the damages.
The question now is, should you also have to sell your home and your belongings to meet the damages? Can anyone really point the blame squarely on you, personally? Who knows where in the process the flaw was? We like to think an "investigation" will find the one person responsible, but that is just Hollywood claptrap, chains of unfortunate events cause serious problems.
Conversely, let's say you have a serious medical problem, and you, personally need millions of dollars in treatment. Should the hospital be able to take your personal belongings? Arguably, yes. But what about your business, your means of livelihood in the first place? Should all the assets be collected, and all of your employees fired because of something you personally , totally unrelated, did?
An LLC goes both ways, it can protect the owner or the company, because it divides the assets and liabilities.
Limited liability is a perfectly reasonable entity. Especially when you start adding on partners and shareholders. There is no reason why something like it would not exist in an ancap society.
Sometimes libertarians think too small, like everyone will have his one-man business, with an abundance of personal responsibility and rugged individualism. This would be a poor, primitive society. That is why we recognize the great economic power of capitalism and markets, because of it's organization and efficiency.