Kling’s analysis is worth reading, and he concludes that the divide between conservatives and libertarians has to do with respect (or lack thereof) for hierarchical authority. Kling does allow for the possibility of a “secular conservative…someone who respects the learning embodied in traditional values and beliefs, without assigning them a divine origin.”
I’m certainly inclined to agree, and I think there are plenty of historical cases of such a “secular” conservatism. The question at issue really is, though, whether there is room for a “religious libertarian.” Kling distinguishes between progressives, libertarians, and conservatives on the basis of their answer to the question of what fuels social progress: movements and leaders, liberty and markets, or religion, respectively.
But it’s not clear to me that any of these options are exclusive. Indeed, one could quite coherently argue that proximate causes of social progress are primarily liberty and markets and that these are means of a common or general sort of divine grace.
The question, then, comes down to whether you think religion and liberty are ultimately and fundamentally opposed. Many secular libertarians suppose that they are. This is a flawed and ultimately untenable position, a development of a particularly closed off and secularized form of Enlightenment rationalism and anthropological arrogance (of course I say this as a Christian believer and as a theologian).
As with so many things, it comes down to a question of first principles. If libertarianism means that any and every human commitment must be subsumed to liberty as an end in itself, then any (other) meaningful religious commitment is excluded.
On the question of respect for authority, we should not be so quick to simply lump all religious adherents, or Christians in particular, into a category that views the state as such as divine. This is a very complicated historiographical and theological question, but the Christian tradition’s ambivalence toward the state is clear. The institution of civil government is most certainly a divine ordinance. This does not amount to a gross or crass blessing of a “divine right of kings” that allows for unlimited or unrestrained use of coercive force in the pursuit of any arbitrary agenda.
Kling’s claim that “the state historically derives from gangs of thugs demanding protection money from settled farmers and herders,” even if taken as true, does not rule out a divine origin. We are talking about two completely different levels of causality, in a way analogous to my previously noted relation of divine grace to liberty and markets. One need not rule out the other. God works through means.
And as I’ve noted previously, we have to take into account a standard of justice or equity, which whether communicated through the natural law or the Ten Commandments restricts legitimate civil authority (see the claim regarding OT Israel as a constitutional monarchy).
Augustine himself writes,
Justice being taken away, then, what are kingdoms but great robberies? For what are robberies themselves, but little kingdoms? The band itself is made up of men; it is ruled by the authority of a prince, it is knit together by the pact of the confederacy; the booty is divided by the law agreed on. If, by the admittance of abandoned men, this evil increases to such a degree that it holds places, fixes abodes, takes possession of cities, and subdues peoples, it assumes the more plainly the name of a kingdom, because the reality is now manifestly conferred on it, not by the removal of covetousness, but by the addition of impunity. Indeed, that was an apt and true reply which was given to Alexander the Great by a pirate who had been seized. For when that king had asked the man what he meant by keeping hostile possession of the sea, he answered with bold pride, “What thou meanest by seizing the whole earth; but because I do it with a petty ship, I am called a robber, whilst thou who dost it with a great fleet art styled emperor.” (City of God, Book IV, Chapter 4, “How Like Kingdoms Without Justice are to Robberies.”)
Kling’s claim regarding the historical origin of governments and Augustine’s description don’t seem that far off from each other. At least in Augustine’s case, he certainly didn’t think that such an account was any evidence against the existence of God or the legitimacy of just civil government.