And civilizations since Aristotle have only lasted a few centuries on average. So when adults look at younger generations and see inevitable decline, they might be correct.
I don't think I implied causation as much as symptoms of decline. In this case we're talking about a large percentage of people who are entering what is historically considered adulthood, 16+, who intend to apply themselves towards a career that (arguably) doesn't offer much utility to anyone. So the ghosts of Ancient Greece would see this as part of the decline of the American civilization and I don't think they would laugh, shrug their shoulders and say, "the kids are alright".
I'm confused as to whether you're saying that a few centuries is a decline or not. When these civilizations were first forming do you believe that the elders would have looked at the youth and seen them as strengthening?