Elsewhere, I make a similar point about religion. The theistic beliefs amount to shibboleths, to tests of loyalty to the group. There are certainly tribal aspects of partisan politics, but there's also a simpler, less conspiratorial explanation, which is the one I give here.
You need only a historical perspective to see the problem with jamming together premodern and modern conservative sentiments. The former conservativism is largely social and religious, the latter is economic and libertarian. The two are bound to be as conflicting as the medieval and modern worlds.