I largely agree that it's often our desire to console ourselves by condeming the contemporary society rather than admitting that we are no longer as young, energetic, and hopeful as we once were that creates the notion of a 'golden age'.The problem with idyllic golden ages is, that they actually never were. The 'Belle Epoque', the Beautiful Epoch, as the era from 1889 to 1914 is called in France and Belgium, is a hindsight after the attrocities of the First World War. But there were lots of problems too. The same for e.g. 'The Golden Sixties'. Reading contemporaneous reports and witnesses from now elderly people, indicate that the 1960 had their economic problems as well, and that some had difficulty to find jobs as well. The streets were not paved with gold, then.
However, I also feel like there are always a good few things left behind when society as a whole gets better with the advancements of culture and technology. Probably we look back fondly at The Belle Epoque more as a progenitor of many modern ideas or trends rather than as a period from which point we have seen the decline of anything significant (e.g. art or quality of life... well, maybe except for clothes since I often wish people still kept their fashion sense from their Victorian or Edwardian age ancestors).
However, I definitely feel that a few things were actually better in the 60s or 80s. Without intending to condemn anyone's personal taste, I believe that the general quality of popular music has seen a striking decline since "The Golden Age of Pop" as people often say. It's not that I think any modern song you may like is somehow inferior to the ones I listen to myself.
It's more about the general atmosphere of the music scene as a whole, or about the ratio between highly original ones and those manufactured like a factory product. Take any arbitrary year between 1963 and 1969 and count how many songs you recognize from the Billboard Top 100 of that year. Then imagine how many songs from the last year you think would be still recognized and loved in 2080.
I have a little 'theory' which I think could explain why the general quality of music has actually declined over the years but I won't delve into it here since it's already become such a long post (sorry, it's one of the incurable habits of mine. I even tend to produce such a wall of text when I write in my native language on any subject.)
So, I think while the world as a whole becoming a better place, there are always a few good things happened to be left behind. As a professional programmer, I by no means resent the advancement of computer technology, for example. But when was the last time you saw children playing outside (at least they don't where I live, not anymore) rather than each silently fiddling one's smartphone forever, like he or she is a part of the network?
Maybe it's just how our society progresses in general, always moving forward while occasionally stumbling, backtracking, or even dropping something from our pockets to be replaced with new things that we find along the way.