There are some obvious additional factors that make it easier or harder for people to 'rub off' on you: sharing a language makes it more likely at distance; belonging to a civilization makes it more likely that you will share at least some values with your ancestors, too. Still, by and large I think it's obvious that you would think of society as progressing morally simply by looking back and discovering that, the further away from yourself you go, the less people agree with your (obviously correct!) moral values.
As a Catholic, I'm inclined to draw a big exception to this general rule, which is that real moral progress is possible if and only if we are moving toward divinely defined rather than human values. Only if we are speaking in this way can we speak sensibly of a real moral progress. Any other sort of talk of moral progress is going to prove to be illusory, a mere flattering of one's self and of those that agree with us.
(There is an inverse argument that most conservative fears of moral crumbling are likewise illusory: if you set any moment in history as your ideal, naturally as you get further away from it values will be more and more different. Thus, both of our usual political viewpoints on morality -- the ones animating progressivism and conservatism -- are wrong.)
I remind you of all of that so that I can present you with this book review.
This is a shocking book, and all the better for it. Many right-thinking and historically well-informed people with a lively sense of justice will be appalled, even outraged, by its central argument, yet it is an argument they will be hard put to refute. In his closing pages, David Rieff states his case with a cogency and directness that are not blunted by the fact that it is framed in the form of a rhetorical question: “is it not conceivable,” he writes, “that were our societies to expend even a fraction of the energy on forgetting that they now do on remembering ... peace in some of the worst places in the world might actually be a step closer?”I once heard a Buddhist argument that held something like: "To say that you have forgiven but not forgotten is to say that you have not forgiven." This is that argument in a developed form.
If you truly did forget, you would lose both any sense of moral progress, and any sense of moral crumbling. What would be left? Would it be enough?