The idea of spontaneous order might be the silliest and most harmful of all.
Simply stated, the idea holds that when groups of individuals are left alone, without government oversight or regulation, they will spontaneously form a social and economic order that is superior in organization, efficiency, and the conveyance of information than an order arranged from the top down through centralized planning.
That's not libertarianism, that's anarchy.
What I see behind libertarianism is more the idea that, should we have a government that exists to enforce order and ensure trades are equal, people are well informed, etc, that people will make better decisions for themselves than the government could make for them through regulations.
For example, imagine a company that makes an unsafe slip and slide. Nobody buys that slip and slide in the future, and the company dies off. That, in theory, should stop companies making unsafe or dangerous products. Combine that with the ability for people to sue.
And, libertarianism purely is not a good thing. Absolutely. Just as pure conservatism, pure liberalism, or pure anything else will likely end up not a good thing. We need a balance and we need a sane, non-idealogical system with which we can make decisions that are best for the situation.
For example, in cases such as drugs that end up killing thousands, you are going to want regulation to ensure companies prove the drugs are safe before sale. Not libertarian, but common sense.
Or, in the case of global warming, because nobody can really claim to cause it or be uniquely effected by it, how can we expect a market to naturally fix it? Oil scarcity it'll deal with amazingly, CO2 emissions not so much. So we create new systems through the government to regulate and stop emissions.
And social libertarianism? Kind of impossible in the case of the "sexual revolution" when marriage itself is already regulated and managed by the government, and rightfully so, who better to hold documents that anyone should be able to access for free?
From my point of view, "sane libertarianism" is all about the art of learning to manipulate people without forcing them to do something directly. Set the environments for the correct decisions to be made, but do not directly force or punish the not-taking of the actions. Cap and trade instead of just cap.