Declinism
Etymology
From decline, Latin declinare, "to bend away, turn aside," plus the "-ism" of a belief system. The word gained currency in debates about the supposed fall of nations and empires, and behavioral writers now use it for the general bias, fed by rosy memory and a bleak-heavy news diet.
noun · /dih-KLY-niz-um/
The predisposition to believe that a society, institution, or era is in decline and that the past was better.
What it names
Why every generation is sure the world is going downhill — the present’s flaws are vivid while the past’s get softened by memory.
Example
His declinism was airtight until the charts showed crime and poverty had both fallen across the decades he mourned.
Related idea
Rosy retrospection is the raw material — remembering the past more fondly than it was — and declinism is the sweeping conclusion drawn from it.