Perhaps I’m particularly attuned to such discussions because the past few months have brought an increase in Rhode Island progressives’ declarations that their goals are evolutionary inevitabilities, but I can’t get the ring of their proclamations out of my ear when listening to somewhat rightish rationalists. Take the following from Julian Sanchez:

[Jonah Goldberg] mocks the idea of a “serious political movement” founded on the slogan “We’re not sure!” But I think this misapprehends one paradoxical aspect of the relationship between doubt and confidence. I know, for example, that science proceeds haltingly, that its conclusions are always open to revision, and indeed, that many of the scientific beliefs of the past have been either rejected or developed to accommodate new facts. And this is precisely why I can be so confident in the scientific enterprise in the aggregate: Because I know there are scores of intelligent and skeptical researchers constantly testing and refining its conclusions. I can be fanatical in my defense of liberal societies, not because (like Islamists) I’m sure they have discovered the One Best Way of Life, but because they embody a process that allows fallible people to seek continual improvement.

The language introduces a bit of muddled expression that is, I think, intended (even if it is not deliberate). Sanchez is confident that science will construct an increasingly correct understanding of the physical world, because its process encourages healthy doubt about any particular finding. Whether or not Sanchez would agree with it, translation of this analogy into the terms of (classically) liberal societies would render thus: Because such societies permit doubt about any particular point of view, they will construct an increasingly correct understanding of the moral world. The “One Best Way of Life” remains implied, if only as an ideal toward which to strive.
That this conflicts with his belief that self-doubting societies can remain strong is emphasized by Sanchez’s omission of certain analogical terms on the social side. Those “intelligent and skeptical researchers” are seeking to improve science; what are the “fallible people” seeking to improve? My guess is that Sanchez would insert “themselves,” rather than “society.”
Science, by its nature, offers the objective metric of ability to explain phenomena. In contrast, the criteria by which we measure progress or deterioration of society and culture are the very things that such as Sanchez would insist remain open to doubt.
Without stating what it is, Sanchez joins the Rhode Island progressives, it seems to me, in seeing his own version of the One Best Way of Life as inevitable. Would he truly remain “fanatical in [his] defense of liberal societies” if their continual improvement appeared to be heading toward, say, Catholic sexual ethics? I suspect he’d be inclined to deny their status as “liberal societies,” even if they continued to embody the very same process.
Cultural processes and criteria also have implications for the part of Goldberg’s response to Sanchez that uses same-sex marriage as an example:

I’m not a passionate opponent to gay marriage — as some close readers have gleened over the years. I favor civil unions and it’s my guess that gay marriage is ultimately inevitable. And yet, I still oppose it. Why? Truth be told, my primary — but not sole — objection isn’t religious. Rather, it’s that, unlike some relevant advocates of same-sex marriage, I am humble and skeptical about the extent of what I can know. I work from the Hayekian assumption that there is a vast amount of social-evolutionary knowledge and utility embedded in traditional marriage that should be respected even if I cannot tell you what it is. … there are some things about which we can’t know all the facts right now. Most social policy failures — and disasters — arise from people working on the assumption that they have all the necessary data at hand. This remains the enduring folly of Progressives who believe they have all the facts they need to redraw the face of society. … In short, my objection to gay marriage isn’t primarily principled in the sense that my objection really has nothing to do with my attitudes toward homosexuality per se. It has to do with my views toward the pace of change itself. Gay marriage is a very, very, new idea. My view/hunch is that implementing it too quickly is a bad idea (for all sorts of obvious and unobvious reasons). More social “evolution” is required. … And, who knows? After a generation of study, comtemplation and debate we may discover that it really is a bad idea after all. Or it may just seem obvious that gays should have been married all along.

I’ve little doubt that I’m failing to observe something that Goldberg actually does intend to say, but his vision of the nature of tradition’s unknowables strikes me as prone to ambiguity. If his claim really is that we can’t know the “social-evolutionary knowledge and utility” of traditional marriage “right now,” but could, through “study, comtemplation and debate,” in a generation, then same-sex marriage proponents would be somewhat justified in noting that they can’t prove a negative (“will not have undesirable consequences”) and dragging out the clock until the deadline for data submissions has passed. Indeed, they’d have some grounds for claiming that we won’t have any new data that hasn’t already been discussed until we’ve allowed same-sex marriage to enter into the society.
In truth, we can’t ever know all of the cultural learning embedded in tradition, and relatedly, its application to modern questions has more to do with sense than with intellect. Regardless of what we, the research-inclined, have been arguing over the past decade, people in this country still can and do conclude that same-sex marriage, as it is being requested right now, should not be grafted onto traditional marriage, as it is understood right now. Some of us can formulate arguments as to why that is or is not a shrewd conclusion, and we all can push and pull marriage toward our preferred understandings. But what time and deference to tradition will shake out are our individual emotions, short-term objectives, and political stratagems.
If same-sex marriage does look more plausible in the light of the midcentury, it will be because marriage and the homosexual subculture will have moved toward each other. That could be good, bad, or a mix of both. If marriage progresses further toward status solely as an institutional contract between adults, without reference to the children whom they may have, that would be bad. If homosexuals increase the degree to which their relationships uphold the ideal assumed in traditional marriage, then that would be good. But over time, and under the specter of tradition, those whose motives are ulterior would either change or seek other methods of acheiving their ends.
That is how fallible people ought to seek continual improvement of the society that they build for themselves — with due understanding that both claims of inevitability and claims of processes’ inherent virtue too often mask a desire to codify import that we fear to be fleeting.