This is a fun line of thinking! I think many people hold the intuition that their sense of right and wrong–unlike, for instance, their way of dressing–is deeply engrained and not subject to the tides of historical fashion. In essence, we expect aesthetics, but not ethics, to change over time.
How wrong we are! Instead, as you (and Steve Pinker) point out, our ethical landscape is ever changing, and the actions we consider moral and immoral have shifted rapidly across the decades. Oftentimes, this reflects the type of “upswing” to which you refer: behaviors that wouldn’t receive any attention 200 years ago–let alone 2,000 years ago–will now get you imprisoned in no time. This upswing doesn’t only apply to behaviors that directly harm others, such as slavery or dueling, but also to those that violate other types of moral principles, such as our desire for purity. Whenever I find myself in Manhattan thinking that its rats and yellow snow are a bit off-putting, I remind myself that just a few centuries ago it would be second nature to perform all manner of bodily functions in the middle of many major cities.
This brings up three related but distinct questions. First, what causes morality to shift over time? It’s difficult to marshal hard evidence to answer this question, because psychological science typically operates on a timescale much shorter than do moral shifts. Nonetheless, Pinker–as well as the philosopher Peter Singer–suggests that our growing aversion to harming others comes from an increase in empathy, or an “expanding moral circle,” under which we feel responsible for the well-being of more and more distant others. This is a powerful idea, but I think it still begs the question as to why moral circles expand. I like Anthony Appiah’s idea that moral shifts often arise from contact with new social groups, and exposure to new social and moral norms (he describes this beautifully in his book The Honor Code). Appiah cites several behaviors, such as Japanese foot binding that suddenly became taboo when its supporters encountered new cultures to which that behavior appeared backwards or strange. In essence, a group’s “ideological circle” expands; they are exposed to a broader world where they are suddenly a tiny moral minority. After that, their morals shift through sheer social pressure.
Second, you cite lots of ways in which moralization is on the upswing; are there any ways in which it’s decreasing? Again, this is a tough question to address with data, but Sara Konrath and her colleagues have done some research that at least connects with it. They’ve found that college students’ levels of empathy for others have steadily decreased over the last 40 years (a finding I wrote about here). This work is all based on answers to questionnaires, so we don’t know, for instance, whether college students over the decades are also less likely to help old ladies across the street, for instance. But even the most mundane interpretation of this result–that students find empathy to be a decreasingly desirable trait (and thus don’t feel pressure to inflate their own empathy on questionnaires)–suggest a shift in our collective moral compass that runs counter to the expanding circle.
Finally, a question I always wonder about and will leave you with: what practices are banal today, but in 100 years will seem unspeakably immoral? This is always a fun (if somewhat disturbing) thought experiment to try, and one that brings our collective moral shiftiness to the surface.