I know what you mean. The good old days are any time that seemed simpler or better. For us, that could mean the 50's, or childhood, or last week. But you are right, there was no time in human history that was perfect, that we can look back on as something being entirely good. We like parts and pieces of "The Good Old Days". People often end up ignoring that those bad things ever happened. In this one instance, I think it is a case of collective optimism for the past, of focusing on the good rather than the bad (which I think runs contrary to human nature in most other respects).