Nostalgia is actually very dangerous, especially considering most people do not actually remember what they think they remember. I'll use the first Star Wars trilogy as an example, because it's a perfect one.
In my memory the movies are very realistic, the special effects were so believable I can even picture myself in the movies. The script was even well done, with smooth transitions and dialog that was smoothly threaded together.
Then I checked out CinemaSins and saw their take on the updated ones. The only reason Lucas did the updates was because nostalgia had fogged his memory.
So I tried watching them today, I got halfway through the first and thought "the books are ten thousand times better." This is because the books feed off the nostalgia, but in reality the movies themselves actually suck by today's standards.
Ignoring the grainy production values, the script was choppy, the plot was sloppy, and the special effects couldn't even pass for real. Star Wars is best left as a memory, because in my memory it's much better than it actually is.
Nostalgia is a problem because the past actually sucked, no matter how fondly you remember it. Your brain will record what it likes best, even altering the memory to make it feel better when you recall it.
This is an effect of all the chemicals in your brain responsible for pleasure, triggering a pleasure chemical makes the memory have a bigger impact on the neural network. So negative events are often forgotten completely, and those which you do recall are plagued with missing bits.
Nostalgia is simply a side effect of the brain preferring pleasure over pain, and the fact that you recall pleasant memories better. So ultimately you cannot trust any of your memories, but more importantly, you can't trust the positive memories of any era.
Those memories with positive enforcement may have negative consequences that you don't recall, which could be dangerous. At the very least, living in the past will make you forget to look forward.