I think this is well-taken, but we should be cautious about the conclusions we draw from it.
It helps to look at a historical analogy. Most people today (I think) consider the 1960s-era civil rights movement to be on the right side of history. We see the racial apartheid system of Jim Crow America as morally repugnant. We see segregated schools and restaurants and buses as morally repugnant. We see flagrant voter suppression as morally repugnant (google “white primaries” if you want to see what flagrant means). And so we see the people who were at the forefront of the civil rights movement as courageous and noble people who took great personal risks to advance a morally righteous cause. Because many of them were.
If you dig deeply into the history of the civil rights movement, though, you will also find a lot of normal human stuff. Infighting. Ideological excess. Extremism. Personal rivalry. Some civil rights organizations of the time were organizationally paralyzed by a very 1960s streak of countercultural anti-authoritarianism that has not aged well. They were often heavily inflected with Marxist revolutionary politics that has not aged well. Many in the movement regarded now revered icons like MLK Jr. as overly cautious establishmentarian sellouts more concerned with their place in history than with social change.
My point is not that the civil rights movement was actually terrible. Nor is it that because the movement was right about school integration, it was also right about the virtues of Maoism. My point is that if you look closely enough, history is always a total goddamned mess. And yet, I still feel pretty comfortable saying that we have made progress on slavery.
So yes, I absolutely agree that many contemporary arguments about moral progress and politics will age terribly, and I doubt it will even take very long. Probably in ten years times, many of the debates of today will look quaint and misguided. But this doesn’t mean we should lapse into a total relativism. It means we need to look at the right scale and also that we should increase our ethical and epistemic humility in direct proportion to the specificity of the moral question we are asking.
These are good questions, and I think the answer generally is yes, we should be disposed to treating the future’s ethics as superior to our own, although we shouldn’t be unquestioning about this.
The place to start is simply to note that obvious fact that moral standards do shift all the time, often in quite radical ways. So at the very least we ought to assume a stance of skepticism toward any particular moral posture, as we have reason to believe that ethics in general are highly contingent, culture-bound, etc.
Then the question becomes whether we have reasons to favor some period’s moral stances over any others. There are a variety of reasons we might do so:
Knowledge has been increasing monotonically, and in recent years extremely rapidly. Much of this knowledge is scientific , technological, or involves other kinds of expertise, and such knowledge does have a moral valence. E.g., we do not believe in witches anymore.
Some of our increasing knowledge is historical and philosophical. The Catholic church did a lot of things in the middle ages that to me seem very bad but seemed to the church at the time morally justified. But I also have access to a lot of historical information about the middle ages, and I can situate the church’s actions in a broader story about politics, empire, religious conflict, etc., that undercuts the church’s moral claims. Other things being equal, we probably are wise to privilege later time periods over earlier time periods because later time periods saw how things turned out. Nazism seemed like a moral imperative to Nazis, but here in 2022, I know how WWII played out. (Spoiler alert: not well!)
The moral changes that have occurred over time are not random, and we can apply meta-ethics to them to try to understand how things have changed. We used to condone slavery and now we abhor it. Is that just happenstance, such that in some alternate history we used to abhor slavery (perhaps for religious reasons) and now embrace it (perhaps because of the logic of capitalism)? Probably not, because across the board the ethical trend has been an extension of rights, franchise, and dignity to widening circles of humans. So we can ask whether we think that is a good ethical trend and draw conclusions about the relative merits of different moral frameworks.
Wealth has also been increasingly more or less monotonically, and insofar as moral behavior might be considered a luxury good, we should suppose that it may be more abundant these days than in past. (This claim deserves a ton of scrutiny. I think it probably is true in some spheres—e.g., gender equality—and maybe less so in others.)
I want to stress that I don’t think these arguments are absolute proof of anything; they are simply reasons we should be disposed to privilege the broad moral leanings of the future over those of the past. Certainly I think over short time spans, many moral shifts are highly contingent and culture-bound. I also think that broad trends might mask a lot of smaller trends that could bounce around much more randomly. And it is absolutely possible that some long-term trends will be morally degrading. For example, I am also not at all sure that long-term technological trends are well-aligned with human flourishing.
It is very easy to imagine that future generations will hold moral positions that we find repugnant. Imagine, for example, that in the far future pregnancy is obsolete. The vast majority of human babies are gestated artificially, which people of the future find safer and more convenient than biological pregnancy. Imagine as a consequence of this that viable fetuses become much more abundant, and people of the future think nothing of raising multiple babies until they are say, three months old, selecting the “best” one based on its personality, sleeping habits, etc., and then painlessly euthanizing the others. Is this a plausible future scenario, or do meta-ethical trends suggest we shouldn’t be concerned about it? If we look into our crystal ball and discover that this is in fact what our ancestors get up to, should we conclude that in the future technological progress will degrade the value of human life in a way that is morally perverse? Or should we conclude instead that technological progress will undermine some of our present-day moral beliefs that aren’t as well-grounded as we think they are? I don’t have a definitive answer, but I would at least suggest that we should strongly consider the latter.