Also, I'm not familiar with the commentary from psychological communities about nostalgia. If they also say that nostalgia blocks those from realizing their mistakes and so on.
In my response I assumed they describe it as a negative because of the first lens, the lens of nostalgia: the bitter of the sweetness that sets in due to ones inability to go back.
Not the second lens, the lens of clear reflection: to realize you're propping up wastes of memories and lies and shrouding the more negative reality of your past through idolization of its simplicity/carefree. To transfigure it.