On a basic level, government is argued to be justified due to the depravity of mankind. Because we humans have such base instincts, Leviathan is necessary to prevent the war of all against all. And it is indeed hard to imagine any sort of order emerging out of anarchy. Without the correcting hand of government, why would anyone cooperate peaceably? How could we trust each other? But what also seems obvious, however, is that most rules governing society are derived not from government fiat but rather from the dictates of human incentives borne out of nature and nurture. No government agency inspects the cleanliness of my kitchen, but I don't think anybody I might invite over for a dinner party fears for their health as a result, for not all constraints on human behavior are written on a piece of paper.
Take marijuana, for example. The stuff's illegal in the United States and yet as far as I can tell, it's hardly a problem for buyers to find sellers, agree on a price, and make an exchange without any concern that the transaction is not under the purview of the FDA, the FTC, or any other member of the alphabet soup who are deemed absolutely essential in so many other exchanges. The same is true of any other black market activities, which are prevalent the world over.
Recognizing this doesn't necessarily argue for anarchy, of course (though I would really like to fly the flag of anarcho-capitalism in front of my house as a subtle show of subversiveness, but it would ironically appear not to be for sale). But what this recognition should do is remind us that in addition to the visible hand of the government, there is a less noticable appendage at work as well.