I think most Americans who think we've gone downhill since 1967 probably really mean that we're either not improving as fast now or are actively going downhill. Or at least I think those positions are more valid (can't say I expect us to be the sole global superpower at the end of my lifetime, and Europe has definitely been catching up to us in terms of per-capita wealth, standard of living, etc.) than saying that we're actually objectively worse off.
Certainly most people would agree that we went mostly uphill in the 60s, 70s, 80s, 90s, and (maybe) the 2000s (I'd say so, but the decade has a stigma attached to it cause of recency bias + the Recession). Just wouldn't make sense to believe that and then say that we're worse off now when we've been improving this whole time.
I think Americans conflate the question "Was life better 50 years ago?" with "Was music/movies/culture better 50 years ago?" because sadly that is all some Americans care about.
I don't really see where this interpretation is coming from. People care a lot about music and movies now, sure, but given that both industries are struggling now (at least relative to the 1970s) I don't really think it really holds up. I don't see people complaining about movies being worse or music being worse so much as how much harder it is to get some stability in a well-paying job without constantly being under pressure (even in well-paying fields like tech, this is hard) or buy some basic things like a house and a car. Life right now seems way more economically chaotic than in the 1950s.
Rather it seems to me that lots of people are just worried about the future and confused about the direction this country is headed. Or at least that's been showing up consistently in polls for nearly a decade regardless of who's in power. Realistically, I think most people would say deep down that our most recent golden age is coming to a close. Our vision of the future has not aged well.
Edited 12/8/2017 06:13:29