Here's a quick review of the most popular "reasons" that liberals, conservatives, intellectuals, janitors, cultural jihadists with brains bathed with wild turkey, roscoes, and the rest will cite you in order to defend the theory that the state is good, wise, at least inevitable, and certainly better than other conceivable alternatives:
1. The Social Contract - This is sort of a political version of the doctrine of "original sin." Supposedly, way back their someplace (with Adam I suppose) we "signed" a deal waiving all of our creator endowed rights and now there's nothing we can do about it. None of those that attempt to justify the state with this excuse can produce a document with signatures, but their faith is undiminished.
2. Divine Right - This theory is actually just as popular today as it ever was. Every time someone tells you to "render unto Caeser," he's saying, "God has ordained the current thugs that control your turf. And when a rival gang moves in and supplants the current extortionists, then, ergo, God has ordained that you shall do whatever they tell you too."
3. Public Goods - This theory holds that if A engages in a certain activity for his own benefit and it turns out that B also benefits from A's activity, then A must forego all activity and benefits derived therefrom because it frosts A so that B is getting free-bies.
The classic example that they use for this in Economics class is fireworks. There's no way for A to prevent B from enjoying A's fireworks, so, ergo without the state (and its thugs) we will never have any fireworks. Adherents to this theory of the state are not deterred by the fact that every 4th of July, private fireworks are launched all over the country.
Their other standard example is protection. They ask, "How will Exxon pay for the aircraft carriers they need to protect their far flung business interests unless the state dips into each paycheck of every wage laborer that lives in America?" Well, they don't actually ask the question like that, do they?
Congress's constitutional powers to raise a navy and lay and collect import duties could be viewed as at least a half assed attempt to combine usage fees (import taxes) on those receiving the service. Our constitutional prohibitions against government standing armies and affirmations of people's militias directly contradicts the "public goods" theory of the state with regard to the issue of protection.
But, like someone said a hundred or so posts back, either you believe in the Enlightenment or you believe in magic. The old magicians told us that the state was inevitable because God said so and/or we all were grafted onto the communal body when we "signed" our social contracts.
Nowadays, we have modern priests (economists) who have graphs and computer printouts that "prove" that without the state there would be no fireworks, protection, street lights, prescription drugs for seniors, or food to eat.
He thought even cleanliness originated in worship or observance rather than agreement or understanding.
His instances are actually observable in pre-history, the Social Contract in action is not. A great response to the Enlightenment thinking.