From Jacob T. Levy’s superb book Rationalism, Pluralism, and Freedom, p 154:
Montesquieu and those who followed him… agreed that… social worlds were not static; manners could become more polished over time, the wealth of nations could grow or decline, agricultural societies could become commercial societies, and so on. But none of these things happened by simple political decree. Governing should usually be done along the grain of such social tendencies and local particularities, occasionally in a way that might counterbalance some undesirable tendency, but never in sheer ignorance of or violence against them. The moeurs, manners, and customs of a society create a cultural reality that one may attempt to guide in one direction or another but that cannot be simply ruled.
Is this not also the key difference between classical liberalism and what we might call high or orthodox libertarianism? The former finds moeurs, or mores, a useful analytic tool, and also a force to be reckoned with in the governing of society. The latter professes itself indifferent to mores and declares that the libertarian political program has nothing at all to do with them. (We’ve just seen Walter Block doing this, his personal mores notwithstanding.)
Consider the authors whom Levy alludes to in the above: The transition from agricultural to commercial society was a chief concern of John Locke’s. We all know who wrote on the wealth of nations. And the improvement of manners over time was a chief concern of Adam Ferguson, David Hume, and even Voltaire. We can see similar concerns animating later classical liberals, including but not limited to John Stuart Mill, who (otherwise rather oddly) conditioned his utilitarianism on a mores-like concern for higher and lower forms of pleasure, and Herbert Spencer, who was very concerned indeed with the development of improved morality over time, and Franz Oppenheimer, who saw the rise of agriculture and then of commerce as crucial developments in the formation of the modern state.
There’s a line to be drawn here, isn’t there? Modern libertarians are often tempted to view these aspects of classical liberalism as so much dross. They are at best a distraction, and more likely a hedge, and – at worst – they are a means of creeping away from the logical implications of so much else in the classical liberal corpus. We are told that the core ideas of classical liberalism would, if followed through consistently, yield something a lot more like Murray Rothbard. Mores do not matter to libertarianism, we are told – and, implicitly: look at the price we pay for even considering them! All that matters is the distinction between coercion and voluntarism.
Not everyone will agree with my suggested line-drawing, and I imagine the largest group of dissenters will be self-identified libertarians who claim, perhaps legitimately, that they do care about mores. Such folk do exist, of course. But the move to discount mores seems both very new as of the twentieth century and one of the more identifying moves of the libertarian movement.
The libertarian rejection of mores as having any analytic salience may also explain some libertarians’ otherwise inexplicable alliances with radical conservatism: If mores don’t matter, then these alliances are not as damning as they appear. But for most people, mores do matter, and that sets up a serious reputational problem (at the very least).
To my mind it needn’t be, and shouldn’t be, either-or. We can of course elaborate on the distinction between coercion and voluntarism, and its implications in a complex society, and on what it means for our laws and our politics, while also recognizing that mores matter in all kinds of ways for the implementation of a good society. Mores delineate which policies appear reasonable for essentially all individuals in a polity. Mores explain why some societies appear to tolerate, or even demand, various forms of coercion more readily than others, and if that’s not important to implementing libertarianism, then nothing is. Development of certain mores would clearly help the libertarian project, even narrowly understood, and development of others would clearly hurt it. To name just one example: The prejudice that condemns wagering now prevents many interesting types of markets from arising. That prejudice came about long before both prediction markets and the policies that have now begun to forbid them. And the prohibition will not go (which of course it should) until the prejudice does. (But how do we get rid of that?)
Mores wouldn’t stop there, either. A libertarian society might cheer for the opening of a vegetable market more strongly than it did for soldiers on parade. Its mores might differ quite radically from many of our current society’s, and not necessarily in ways that libertarians themselves can predict. It is odd, or it should be odd, not to ponder them along the way.
Do note that this concern for mores does not necessarily entail any ideological softening on the distinction between free and coerced action, between voluntary and unrequited transfers. The two dimensions are completely orthogonal to one another. But I don’t think one should be indifferent to either of them.
 The word mores is often left untranslated as the French word moeurs, for reasons I’ve never understood. As a speaker of both languages, the English word seems perfectly adequate to me. It denotes the settled attitudes, manners, and customs of a society, exactly as the French word does. Frequently but not always, mores are hard to articulate. Individuals often constitute exceptions to a society’s mores, but those who deploy the term can usefully refer back to the general. Discussions of national character often ensue, as when someone describes the United States as being a particularly enterprising nation, or a particularly religious one. Or a particularly violent one. There are dangers of stereotypes hereabouts, but there is also useful empirical work to be done, and mores also touch on questions of tacit knowledge and trust, in ways I won’t get into here.
 Ayn Rand is the odd exception, as she so often is. Rand very clearly thought that things like manners and customs were important, and that mores followed necessarily (though perhaps unexaminedly) from values that individuals held. Whether those values were held rationally or not, mores mattered to her, and I suspect that an important part of building an Objectivist society, as she saw it, would lie in the identification of the various premises on which our mores were based, and on their improvement. One might even say that when Rand writes of a sense of life, she means the totality of one’s mores, insofar as they inform how we are to think about the human condition. Which of course they do. A lot. In this she seems to lie rather closer to classical liberals, and her insistence that she was not a libertarian takes on a new dimension.